OData Extension for Data Aggregation Ver

OData Extension for Data Aggregation Version 4.0
OData Extension for Data Aggregation Version 4.0
Committee Specification 04
18 November 2025
This stage:
(Authoritative)
Previous stage:
(Authoritative)
Latest stage:
(Authoritative)
Technical Committee:
OASIS Open Data Protocol (OData) TC
Chairs:
Ralf Handl (
[email protected]
),
SAP SE
Michael Pizzo (
[email protected]
),
Microsoft
Editors:
Ralf Handl (
[email protected]
),
SAP SE
Hubert Heijkers (
[email protected]
),
IBM
Gerald Krause (
[email protected]
),
SAP SE
Michael Pizzo (
[email protected]
),
Microsoft
Heiko Theißen (
[email protected]
),
SAP SE
Martin Zurmuehl (
[email protected]
),
SAP SE
Additional artifacts:
This document is one component of a Work Product that also includes:
ABNF components:
OData Aggregation ABNF Construction Rules Version 4.0 and OData Aggregation ABNF Test Cases
OData Aggregation Vocabulary:
Related work:
This specification is related to:
OData Version 4.01
. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. A multi-part Work Product which includes:
OData Version 4.01 Part 1: Protocol
. Latest stage:
OData Version 4.01 Part 2: URL Conventions
. Latest stage:
ABNF components: OData ABNF Construction Rules Version 4.01 and OData ABNF Test Cases
OData Vocabularies Version 4.0
. Edited by Michael Pizzo, Ralf Handl, and Ram Jeyaraman. Latest stage:
OData Common Schema Definition Language (CSDL) JSON Representation Version 4.01
. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. Latest stage:
OData Common Schema Definition Language (CSDL) XML Representation Version 4.01
. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. Latest stage:
OData JSON Format Version 4.01
. Edited by Ralf Handl, Mike Pizzo, and Mark Biamonte. Latest stage:
Abstract:
This specification adds basic grouping and aggregation functionality (e.g. sum, min, and max) to the Open Data Protocol (OData) without changing any of the base principles of OData.
Status:
This document was last revised or approved by the OASIS Open Data Protocol (OData) TC on the above date. The level of approval is also listed above. Check the “Latest stage” location noted above for possible later revisions of this document. Any other numbered Versions and other technical work produced by the Technical Committee (TC) are listed at
TC members should send comments on this specification to the TC’s email list. Any individual may submit comments to the TC by sending email to
[email protected]
. Please use a Subject line like “Comment on OData Data Aggregation”.
This specification is provided under the
RF on RAND Terms Mode
of the
OASIS IPR Policy
, the mode chosen when the Technical Committee was established. For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the TC’s web page (
).
Note that any machine-readable content (
Computer Language Definitions
) declared Normative for this Work Product is provided in separate plain text files. In the event of a discrepancy between any such plain text file and display content in the Work Product’s prose narrative document(s), the content in the separate plain text file prevails.
Key words:
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in BCP 14
RFC2119
and
RFC8174
when, and only when, they appear in all capitals, as shown here.
Citation format:
When referencing this specification the following citation format should be used:
[OData-Data-Agg-v4.0]
OData Extension for Data Aggregation Version 4.0
. Edited by Ralf Handl, Hubert Heijkers, Gerald Krause, Michael Pizzo, Heiko Theißen, and Martin Zurmuehl. 18 November 2025. OASIS Committee Specification 04.
. Latest stage:
Notices
Copyright © OASIS Open 2025. All Rights Reserved.
Distributed under the terms of the OASIS
IPR Policy
The name “OASIS” is a trademark of
OASIS
, the owner and developer of this specification, and should be used only to refer to the organization and its official outputs.
For complete copyright information please see the full Notices section in an Appendix
below
Table of Contents
1 Introduction
1.1 Changes from Earlier Versions
1.2 Glossary
1.2.1 Definitions of Terms
1.2.2 Acronyms and Abbreviations
1.2.3 Document Conventions
2 Overview
2.1 Example Data Model
2.2 Example Data
2.3 Example Use Cases
3 System Query Option
$apply
3.1 Fundamentals of Input and Output Sets
3.1.1 Type, Structure and Context URL
3.1.2 Sameness and Order
3.1.3 Evaluation of Data Aggregation Paths
3.2 Basic Aggregation
3.2.1 Transformation
aggregate
3.2.1.1 Aggregation Algorithm
3.2.1.2 Keyword
as
3.2.1.3 Aggregation Methods
3.2.1.3.1 Standard Aggregation Method
sum
3.2.1.3.2 Standard Aggregation Method
min
3.2.1.3.3 Standard Aggregation Method
max
3.2.1.3.4 Standard Aggregation Method
average
3.2.1.3.5 Standard Aggregation Method
countdistinct
3.2.1.3.6 Custom Aggregation Methods
3.2.1.4 Aggregate Expression
$count
3.2.2 Transformation
concat
3.2.3 Transformation
groupby
3.2.3.1 Simple Grouping
3.3 Transformations Producing a Subset
3.3.1 Top/bottom transformations
3.3.1.1 Transformations
bottomcount
and
topcount
3.3.1.2 Transformations
bottompercent
and
toppercent
3.3.1.3 Transformations
bottomsum
and
topsum
3.3.2 Transformation
filter
3.3.3 Transformation
orderby
3.3.4 Transformation
3.3.5 Transformation
skip
3.3.6 Transformation
top
3.3.7 Stable Total Order Before
$skip
and
$top
3.4 One-to-One Transformations
3.4.1 Transformation
identity
3.4.2 Transformation
compute
3.5 Transformations Changing the Input Set Structure
3.5.1 Transformations
join
and
outerjoin
3.6 Expressions Evaluable on a Collection
3.6.1 Function
aggregate
3.6.2 Expression
$count
3.7 Function
isdefined
3.8 Evaluating
$apply
as an Expand and Select Option
3.9 ABNF for Extended URL Conventions
4 Cross-Joins and Aggregation
5 Vocabulary for Data Aggregation
5.1 Aggregation Capabilities
5.2 Custom Aggregates
5.3 Context-Defining Properties
5.4 Annotation Example
5.5 Hierarchies
5.5.1 Recursive Hierarchy
5.5.1.1 Hierarchy Functions
5.5.2 Hierarchy Examples
5.6 Functions on Aggregated Entities
6 Hierarchical Transformations
6.1 Common Parameters for Hierarchical Transformations
6.2 Hierarchical Transformations Producing a Subset
6.2.1 Transformations
ancestors
and
descendants
6.2.2 Transformation
traverse
7 Examples
7.1 Requesting Distinct Values
7.2 Standard Aggregation Methods
7.3 Requesting Expanded Results
7.4 Requesting Custom Aggregates
7.5 Aliasing
7.6 Combining Transformations per Group
7.7 Model Functions as Set Transformations
7.8 Controlling Aggregation per Rollup Level
7.9 Aggregation in Recursive Hierarchies
7.10 Maintaining Recursive Hierarchies
7.11 Transformation Sequences
8 Conformance
A References
A.1 Normative References
B Acknowledgments
B.1 Special Thanks
B.2 Participants
C Revision History
D Notices
1 Introduction
This specification adds aggregation functionality to the Open Data Protocol (OData) without changing any of the base principles of OData. It defines semantics and a representation for aggregation of data, especially:
Semantics and operations for querying aggregated data,
Results format for queries containing aggregated data,
Vocabulary terms to annotate what can be aggregated, and how.
1.1 Changes from Earlier Versions
Compared to the previous stage
[OData-Data-Agg-v4.0]
OASIS Committee Specification 03, this version makes the following restrictions.
Section
Restriction
After
section 3.2.1.4
Keyword
from
removed
After
section 3.2.3.1
Grouping with
rollup
removed
After
section 3.4.2
Transformation
addnested
removed
After
section 3.5.1
Transformation
nest
removed
Before
section 5.5.1
Leveled Hierarchy removed
Section 6.1
Optional parameter
$S$
removed
Section 6.2.2
Restricted to single-valued
ParentNavigationProperty
After
section 6.2.2
Grouping with
rolluprecursive
removed
1.2 Glossary
1.2.1 Definitions of Terms
This specification defines the following terms:
Aggregatable Expression
– an
expression
not involving term casts and resulting in a value of a complex or entity or an
aggregatable primitive type
Aggregate Expression
– argument of the
aggregate
transformation
or
function
defined in
section 3.2.1.1
Aggregatable Primitive Type
– a primitive type other than
Edm.Stream
or subtypes of
Edm.Geography
or
Edm.Geometry
Data Aggregation Path
– a path that consists of one or more segments joined together by forward slashes (
). Segments are names of declared or dynamic structural or navigation properties, or type-cast segments consisting of the (optionally qualified) name of a structured type that is derived from the type identified by the preceding path segment to reach properties declared by the derived type.
Expression
– derived from the
commonExpr
rule (see
OData-ABNF
Single-Valued Property Path
– property path ending in a single-valued primitive, complex, or navigation property
1.2.2 Acronyms and Abbreviations
The following non-exhaustive list contains variable names that are used throughout this document:
$A,B,C$
– collections of instances
$H$
– hierarchical collection
$H'$
– subset of nodes from a hierarchical collection
$u,v,w$
– instances in a collection
$x$
– an instance in a hierarchical collection, called a node
$p,q,r$
– paths
$T$
– transformation sequence
$α$
aggregate expression
, defined in
section 3.2.1.1
$\Gamma(A,p)$
– the collection that results from evaluating a
data aggregation path
$p$
relative to a collection
$A$
, defined in
section 3.1.3
$γ(u,p)$
– the collection that results from evaluating a
data aggregation path
$p$
relative to an instance
$u$
, defined in
section 3.1.3
$\Pi_G(s)$
– a transformation of a collection that injects grouping properties into every instance of the collection, defined in
section 3.2.3.1
$σ(x)$
– instance containing a grouping property that represents a node
$x$
, defined in
section 6.2.2
1.2.3 Document Conventions
Keywords defined by this specification use
this monospaced font
Some sections of this specification are illustrated with non-normative examples.
Example 1: text describing an example uses this paragraph style
Non-normative examples use this paragraph style.
All examples in this document are non-normative and informative only. Examples labeled with ⚠ contain advanced concepts or make use of keywords that are defined only later in the text, they can be skipped at first reading.
All other text is normative unless otherwise labeled.
Paragraphs labeled 🚧 in this version of the specification contain restrictions that were not made in
[OData-Data-Agg-v4.0]
OASIS Committee Specification 03. Also, some sections of
[OData-Data-Agg-v4.0]
OASIS Committee Specification 03 are omitted from this version. In later OASIS standard versions these restrictions may be lifted again and the omitted sections reintroduced.
The ABNF rules
OData-ABNF
have been simplified in this version to reflect these restrictions. Also, some members of the OData Aggregation Vocabulary
OData-VocAggr
have been omitted from this version. These members are referenced by
[OData-Data-Agg-v4.0]
OASIS Committee Specification 03 but not by this version.
2 Overview
Open Data Protocol (OData) services expose a data model that describes the schema of the service in terms of the Entity Data Model (EDM, see
OData-CSDL
) and then allows for querying data in terms of this model. The responses returned by an OData service are based on that data model and retain the relationships between the entities in the model.
Extending the OData query features with simple aggregation capabilities avoids cluttering OData services with an exponential number of explicitly modeled “aggregation level entities” or else restricting the consumer to a small subset of predefined aggregations.
Adding the notion of aggregation to OData without changing any of the base principles in OData has two aspects:
Means for the consumer to query aggregated data on top of any given data model (for sufficiently capable data providers)
Means for the provider to annotate what data can be aggregated, and in which way, allowing consumers to avoid asking questions that the provider cannot answer
Implementing any of these two aspects is valuable in itself independent of the other, and implementing both provides additional value for consumers. The provided aggregation annotations help a consumer understand more of the data structure looking at the service’s exposed data model. The query extensions allow the consumers to explicitly express the desired aggregation behavior for a particular query. They also allow consumers to formulate queries that utilize the aggregation annotations.
2.1 Example Data Model
Example 2: The following diagram depicts a simple model that is used throughout this document.
The
Amount
property in the
Sale
entity type is an
aggregatable property
, and the properties of the related entity types are groupable. These can be arranged in hierarchies, for example:
Product hierarchy based on
groupable
properties of the
Category
and
Product
entity types
Customer hierarchy based on
Country
and
Customer
Time hierarchy based on
Year
Month
, and
Date
SalesOrganization
hierarchy
based on the recursive association to itself
In the context of Online Analytical Processing (OLAP), this model might be described in terms of a Sales “cube” with an Amount “measure” and three “dimensions”. This document will avoid such terms, as they are heavily overloaded.
Query extensions and descriptive annotations can be applied to normalized schemas as well as partly or fully denormalized schemas.
Example 3: The following diagram depicts a denormalized schema for the simple model.
Sale
Sales
ID: Edm.String {id}
Amount: Edm.Decimal
Category
CategoryID: Edm.String
CategoryName: Edm.String
Product
ProductID: Edm.String
ProductName: Edm.String
ProductColor: Edm.String
ProductTaxRate: Edm.Decimal
Food
FoodProductRating: Edm.Byte
Non-Food
NonFoodProductRatingClass: Edm.String
Sales Organization
SalesOrganizationID: Edm.String
SalesOrganizationName: Edm.String
SalesOrganizationSuperordinateID: Edm.String
Time
TimeDate: Edm.Date
TimeMonth: Edm.String
TimeQuarter: Edm.String
TimeYear: Edm.Int16
Customer
CustomerID: Edm.String
CustomerName: Edm.String
CustomerCountry: Edm.String
2.2 Example Data
Example 4: The following entity sets and sample data will be used to further illustrate the capabilities introduced by this extension.
Products
ID
Category
Name
Color
TaxRate
P1
PG1
Sugar
White
0.06
P2
PG1
Coffee
Brown
0.06
P3
PG2
Paper
White
0.14
P4
PG2
Pencil
Black
0.14
Food
Rating
n/a
n/a
Non-Food
RatingClass
n/a
n/a
average
Time
Date
Month
Quarter
Year
2022-01-01
2022-01
2022-1
2022
2022-04-01
2022-04
2022-2
2022
2022-04-10
2022-04
2022-2
2022
Categories
ID
Name
PG1
Food
PG2
Non-Food
Sales Organizations
ID
Superordinate
Name
Sales
Corporate Sales
US
Sales
US
US West
US
US West
US East
US
US East
EMEA
Sales
EMEA
EMEA Central
EMEA
EMEA Central
Customers
ID
Name
Country
C1
Joe
USA
C2
Sue
USA
C3
Sue
Netherlands
C4
Luc
France
Sales
ID
Customer
Time
Product
Sales Organization
Amount
C1
2022-01-03
P3
US West
C1
2022-04-10
P1
US West
C1
2022-08-07
P2
US West
C2
2022-01-03
P2
US East
C2
2022-11-09
P3
US East
C3
2022-04-01
P1
EMEA Central
C3
2022-08-06
P3
EMEA Central
C3
2022-11-22
P3
EMEA Central
Legend
Property
Key
Navigation Property
2.3 Example Use Cases
Example 5: In the example model, one prominent use case is the relation of customers to products. The first question that is likely to be asked is: “Which customers bought which products?”
This leads to the second more quantitative question: “Who bought how much of what?”
The answer to the second question typically is visualized as a cross-table:
Food
Non-Food
Sugar
Coffee
Paper
USA
14
12
Joe
Sue
Netherlands
Sue
The data in this cross-table can be written down in a shape that more closely resembles the structure of the data model, leaving cells empty that have been aggregated away:
Customer/Country
Customer/Name
Product/Category/Name
Product/Name
Amount
USA
Joe
Non-Food
Paper
USA
Joe
Food
Sugar
USA
Joe
Food
Coffee
USA
Sue
Food
Coffee
USA
Sue
Non-Food
Paper
Netherlands
Sue
Food
Sugar
Netherlands
Sue
Non-Food
Paper
USA
Food
Sugar
USA
Food
Coffee
12
USA
Non-Food
Paper
Netherlands
Food
Sugar
Netherlands
Non-Food
Paper
USA
Joe
Food
USA
Joe
Non-Food
USA
Sue
Food
USA
Sue
Non-Food
Netherlands
Sue
Food
Netherlands
Sue
Non-Food
USA
Food
14
USA
Non-Food
Netherlands
Food
Netherlands
Non-Food
Note that this result contains seven fully qualified aggregate values, followed by fifteen rollup rows with subtotal values.
3 System Query Option
$apply
set transformation
transformation
for short) is an operation on an input set that produces an output set. A
transformation sequence
is a sequence of set transformations, separated by forward slashes to express that they are consecutively applied. A transformation sequence may be invoked using the system query option
$apply
. The input set of the first set transformation is the collection addressed by the resource path. The output set of each set transformation is the input set for the next set transformation. The output set of the last set transformation in the transformation sequence invoked by the system query option
$apply
is the result of
$apply
. This is consistent with the use of service-defined bound and composable functions in path segments. Set transformations may also appear as a parameter of certain other set transformations defined below.
The system query option
$apply
MUST NOT be used if the resource path addresses a single instance.
The system query option
$apply
is evaluated first, then the other system query options are evaluated, if applicable, on the result of
$apply
, see
OData-Protocol, section 11.2.1
. Stability across requests for system query options
$top
and
$skip
OData-Protocol, section 11.2.6.3
is defined in
section 3.3.7
Each set transformation:
carries over the input type to the output set such that it fits into the data model of the service.
can mark certain navigation properties and stream properties for
expansion by default
, that is, they are expanded in the result of
$apply
in the absence of an
$expand
query option.
may produce an output set with a different number of instances than the input set.
does not necessarily guarantee that all properties of the instances in the output set have a well-defined value.
Instances of an output set can contain structural and navigation properties, which can be declared or dynamic, as well as instance annotations.
The allowed set transformations are defined in this section as well as in the section on
Hierarchical Transformations
Service-defined bound functions that take a collection of instances of a structured type as their binding parameter and return a collection of instances of a structured type MAY be used as set transformations within
$apply
. Further transformations can follow the bound function. The parameter syntax for bound function segments is identical to the parameter syntax for bound functions in resource path segments or
$filter
expressions. See
section 7.7
for an example.
Parameter aliases
OData-URL, section 5.3
can be used inside the value of
$apply
wherever the ABNF rule
applyTrafo
OData-ABNF
is reduced to a
commonExpr
OData-URL, section 5.1.1
or a
collectionExpr
section 3.6
).
If a data service that supports
$apply
does not support it on the collection identified by the request resource path, it MUST fail with
501 Not Implemented
and a meaningful human-readable error message.
On resource paths ending in
/$count
the system query option
$apply
is evaluated on the set identified by the resource path without the
/$count
segment, the result is the plain-text number of items in the result of
$apply
. This is similar to the combination of
/$count
and
$filter
During serialization of the result of
$apply
declared properties and dynamic properties are represented as defined by the response format. Other properties have been aggregated away and are not represented in the response. The entities returned in the request examples in the following sections that involve aggregation are therefore transient.
3.1 Fundamentals of Input and Output Sets
The definitions of italicized terms made in this section are used throughout this text, always with a hyperlink to this section.
3.1.1 Type, Structure and Context URL
All input sets and output sets in one transformation sequence are collections of the
input type
, that is the entity type or complex type of the first input set, or in other words, of the resource to which the transformation sequence is applied. The input type is determined by the entity model element identified within the metadata document by the context URL of that resource
OData-Protocol, section 10
. Individual instances in an input or output set can have a subtype of the input type. (See
example 65
.) The transformation sequence given as the
$apply
system query option is applied to the resource addressed by the resource path. The transformations defined below can have nested transformation sequences as parameters, these are then applied to resources that can differ from the current input set.
The
structure
of an instance that occurs in an input or output set is defined by the names of the structural and navigation properties that the instance contains. Instances of an input type can have different structures, subject to the following rules:
Declared properties of the input type or a nested or related type thereof or of a subtype of one of these MUST have their declared type and meaning when they occur in an input or output set.
Single- or collection-valued primitive properties addressed by a property path starting at a non-transient entity MUST keep their values from the addressed resource path collection throughout the transformation sequence. Likewise, single- or collection-valued navigation property paths starting at a non-transient entity MUST keep addressing the same non-transient entities as in the addressed resource path collection.
Instances in an output set need not have all declared or dynamic properties that occurred in the input set.
Instances in an output set can have dynamic properties that did not occur in the input set. The name for such a dynamic property is called an
alias
, it is a simple identifier (see
OData-CSDL, section 15.2
). Aliases MUST differ from names of declared properties in the input type, from names of properties in the first input set, and from names of properties in the current input set. Aliases in one collection MUST also differ from each other.
Instances in an output set that have all key properties of an entity also have the metadata associated with that entity, such as entity-id, read and edit URL (defined in
OData-Protocol, section 4
) and ETag (defined in
OData-Protocol, section 11.4.1.2
) as well as relations to other entities
OData-Protocol, section 11.2.7
Here is an overview of the structural changes made by different transformations:
During
aggregation
, many instances are replaced by one instance, properties that represent the aggregation level are retained, and others are replaced by dynamic properties holding the aggregate value of the many instances or a transformed copy of them.
During
compute
, dynamic properties are added to each instance.
During
join
, one instance with a collection of related instances is replaced by many copies, each of which is related via a dynamic property to one of the related instances.
During
concatenation
, the same instances are transformed multiple times and the output sets with their potentially different structures are concatenated.
An output set thus consists of instances with different structures. This is the same situation as with a collection of an open type (
OData-CSDL, section 6.3
and
OData-CSDL, section 9.3
) and it is handled in the same way.
If the first input set is a collection of entities from a given entity set, then so are all input sets and output sets in the transformation sequence. The
{select-list}
in the context URL
OData-Protocol, section 10
MUST describe only properties that are present or annotated as absent (for example, if
Core.Permissions
is
None
OData-Protocol, section 11.2.2
) in all instances of the collection, after applying any
$select
and
$expand
system query options. The
{select-list}
SHOULD describe as many such properties as possible, even if the request involves a concatenation that leads to a non-homogeneous structure. If the server cannot determine any such properties, the
{select-list}
MUST consist of just the instance annotation
AnyStructure
defined in the
Core
vocabulary
. (See
example 66
.)
3.1.2 Sameness and Order
Input sets and output sets are not sets of instances in the mathematical sense but collections, because the same instance can occur multiple times in them. In other words: A collection contains values (which can be instances of structured types or primitive values), possibly with repetitions. The occurrences of the values in the collection form a set in the mathematical sense. The
cardinality
of a collection is the total number of occurrences in it. When this text describes a transformation algorithmically and stipulates that certain steps are carried out
for each occurrence
in a collection, this means that the steps are carried out multiple times for the same value if it occurs multiple times in the collection.
A collection addressed by the resource path is returned by the service either as an ordered collection
OData-Protocol, section 11.4.9
or as an unordered collection. The same applies to collections that are nested in or related to the addressed resource as well as to collections that are the result of evaluating an expression starting with
$root
, which occur, for example, as the first parameter of a
hierarchical transformation
But when such a collection is transformed by the
$apply
system query option, additional cases can arise that are neither ordered nor totally unordered. For example, the
groupby
transformation retains any order within a group but not between groups.
⚠ Example 6: Request the top 10 sales per customer. The processing of the request can be parallelized per customer and the responses per customer can be interleaved in the overall response. This means that for any given customer, their top 10 sales appear in the desired order, though not consecutively.
GET /service/Sales?$apply=groupby((Customer),orderby(Amount desc)/top(10))
For every transformation defined in the following sections, it will be specified how it orders its output set, based on the order of its input set. The order of the last output set can be further influenced by a
$orderby
system query option before it is observed in the response payload.
An order of a collection is more precisely defined as follows: Given two different occurrences
$u_1$
and
$u_2$
in a collection, which may be of the same value or of different values,
$u_1$
precedes
$u_2$
or
$u_2$
precedes
$u_1$
, but not both. It can be neither, in which case the relative order of
$u_1$
and
$u_2$
does not matter. If
$u_1$
precedes
$u_2$
and
$u_2$
precedes
$u_3$
, then
$u_1$
also precedes
$u_3$
, and
$u_1$
never precedes
$u_1$
. (This is a partial order in the mathematical sense defined on the set of occurrences.)
When transformations are defined in the following sections, the algorithmic description sometimes contains an
order-preserving loop
over a collection. Such a loop processes the occurrences in an order chosen by the service in such a way that
$u_1$
is processed before
$u_2$
whenever
$u_1$
precedes
$u_2$
. Likewise, in an
order-preserving sequence
$u_1,…,u_n$
we have
$iwhenever
\(u_i$
precedes
$u_j$
A collection can be
stable-sorted
by a list of expressions. In the stable-sorted collection an occurrence
$u_1$
precedes
$u_2$
if and only if either
$u_1$
precedes
$u_2$
according to the rules of
OData-Protocol, section 11.2.6.2
or
these rules do not determine a precedence in either direction between
$u_1$
and
$u_2$
but
$u_1$
preceded
$u_2$
in the collection before the sort.
Stable-sorting of an ordered collection produces another ordered collection. A stable-sort does not necessarily produce a total order, the sorted collection may still contain two occurrences whose relative order does not matter. The transformation
orderby
performs a stable-sort.
The output set of a
basic aggregation
transformation can contain instances of an entity type without entity-id. After a
concat
transformation, different occurrences of the same entity can differ in individual non-declared properties. To account for such cases, the definition of sameness given in
OData-URL, section 5.1.1.1.1
is refined here. Instances of structured types are
the same
if
both are instances of complex types and both are null or both have the same structure and same values with null considered different from absent or
both are instances of entity types without entity-id (see
OData-Protocol, section 4.3
) and both are null or both have the same structure and same values with null considered different from absent (informally speaking, they are compared like complex instances) or
(1) both are instances of the same entity type with the same entity-id (non-transient entities, see
OData-Protocol, section 4.1
) and (2) the structural and navigation properties contained in both have the same values (for non-primitive properties the sameness of values is decided by a recursive invocation of this definition).
If this is fulfilled, the instances are called
complementary representations of the same non-transient entity
. If this case is encountered at some recursion level while the sameness of non-transient entities
$u_1$
and
$u_2$
is established, a merged representation of the entity
$u_1=u_2$
exists that contains all properties of
$u_1$
and
$u_2$
. But if the instances both occur in the last output set, services MUST represent each with its own structure in the response payload.
If the first condition is fulfilled but not the second, the instances are not the same and are called
contradictory representations of the same non-transient entity
. (
Example 84
describes a use case for this.)
Collections are
the same
if there is a one-to-one correspondence
$f$
between them such that
corresponding occurrences are of the same value and
an occurrence
$u_1$
precedes another occurrence
$u_2$
if and only if the occurrence
$f(u_1)$
precedes the occurrence
$f(u_2)$
, where the occurrences
$u_1$
and
$u_2$
may be of the same value or of different values. (A one-to-one correspondence with this second property is called
order-preserving
.)
3.1.3 Evaluation of Data Aggregation Paths
This document specifies how a
data aggregation path
that occurs in a request is evaluated by the service. If such an evaluation fails, the service MUST reject the request.
For a data aggregation path to be a common expression according to
OData-URL, section 5.1.1
, its segments must be single-valued with the possible exception of the last segment, and it can then be evaluated relative to an instance of a structured type. For the transformations defined in this document, a data aggregation path can also be evaluated relative to a collection
$A$
, even if it has arbitrary collection-valued segments itself.
To this end, the following notation is used in the subsequent sections: If
$A$
is a collection and
$p$
a data aggregation path, optionally followed by a type-cast segment, the result of such a path evaluation is denoted by
$\Gamma(A,p)$
and defined as the unordered concatenation, possibly containing repetitions, of the collections
$γ(u,p)$
for each
$u$
in
$A$
that is not null. The function
$γ(u,p)$
takes a non-null value and a path as arguments and returns a collection of instances of structured types or primitive values, depending on the type of the final segment of
$p$
. It is recursively defined as follows:
If
$p$
is an empty path, let
$B$
be a collection with
$u$
as its single member and continue with step 9.
Let
$p_1$
be the first segment of
$p$
and
$p_2$
the remainder, if any, such that
$p$
equals the concatenated path
$p_1/p_2$
If
$p_1$
is a type-cast segment and
$u$
is of its type or a subtype thereof, let
$v=u$
and continue with step 8.
If
$p_1$
is a type-cast segment and
$u$
is not of its type or a subtype thereof, let
$B$
be an empty collection and continue with step 9. (This rule follows
OData-URL, section 4.11
rather than
OData-CSDL, section 14.4.1.1
.)
Otherwise,
$p_1$
is a non-type-cast segment. If
$u$
does not contain a structural or navigation property
$p_1$
, let
$B$
be an empty collection and continue with step 9.
If
$p_1$
is single-valued, let
$v$
be the value of the structural or navigation property
$p_1$
in
$u$
. If
$v$
is null, let
$B$
be an empty collection and continue with step 9; otherwise continue with step 8.
Otherwise,
$p_1$
is collection-valued. Let
$C$
be the collection addressed by the structural or navigation property
$p_1$
in
$u$
, and let
$B=\Gamma(C,p_2)$
. Then continue with step 9.
Let
$B=γ(v,p_2)$
Return
$B$
This notation is extended to the case of an empty path
$e$
by setting
$\Gamma(A,e)=A$
with null values removed. Note the collections returned by
$\Gamma$
and
$γ$
never contain the null value. Also, every instance
$u$
in
$\Gamma(A,p)$
occurs also in
$A$
or nested into
$A$
, therefore an algorithmic step like “Add a dynamic property to each
$u$
in
$\Gamma(A,p)$
” effectively changes
$A$
3.2 Basic Aggregation
3.2.1 Transformation
aggregate
3.2.1.1 Aggregation Algorithm
The
aggregate
transformation takes a comma-separated list of one or more
aggregate expressions
as parameters and returns an output set with a single instance of the
input type
without entity-id containing one property per aggregate expression, representing the aggregated value of the input set.
An aggregate expression MUST have one of the types listed below. To compute the value of the property for a given aggregate expression, the
aggregate
transformation first determines a collection
$A$
of instances of structured types or primitive values, based on the input set of the
aggregate
transformation, and a path
$p$
that occurs in the aggregate expression. Let
$p_1$
denote a
data aggregation path
with single- or collection-valued segments and
$p_2$
a type-cast segment. Depending on its type, the aggregate expression contains a path
$p=p_1$
or
$p=p_2$
or
$p=p_1/p_2$
. Each type of aggregate expression defines a function
$f(A)$
which the aggregate transformation evaluates to obtain the property value.
The property is a dynamic property, except for a special case in type 4. In types 1 and 2, the aggregate expression MUST end with the keyword
with
and an aggregation method
$g$
. The aggregation method also determines the type of the dynamic property. In types 1, 2, and 3 the aggregate expression MUST, and in type 4 it MAY, be followed by the keyword
as
and an
alias
, which is then the name of the dynamic property.
Types of aggregate expressions:
A path
$p=p_1$
or
$p=p_1/p_2$
where the last segment of
$p_1$
has a complex or entity or
aggregatable primitive type
whose values can be aggregated using the specified
aggregation method
$g$
, or
$p=p_2$
if the input set can be aggregated using the
custom aggregation method
$g$
Let
$f(A)=g(A)$
An
aggregatable expression
whose values can be aggregated using the specified
aggregation method
$g$
Let
$f(A)=g(B)$
where
$B$
is the collection consisting of the values of the aggregatable expression evaluated relative to
each occurrence
in
$A$
with null values removed from
$B$
. In this type,
$p$
is absent.
A path
$p/{\tt\$count}$
(see
section 3.2.1.4
) with optional prefix
$p/{}$
where
$p=p_1$
or
$p=p_2$
or
$p=p_1/p_2$
Let
$f(A)$
be the
cardinality
of
$A$
A path
$p/c$
consisting of an optional prefix
$p/{}$
with
$p=p_1$
or
$p=p_1/p_2$
where the last segment of
$p_1$
has a structured type or
$p=p_2$
, and a
custom aggregate
$c$
defined on the collection addressed by
$p$
Let
$f(A)=c(A)$
. If computation of the custom aggregate fails, the service MUST reject the request. In the absence of an alias:
The name of the property is the name of the custom aggregate.
The property is a dynamic property whose type is determined by the custom aggregate, unless there is a declared property with that name. The latter case is allowed by the
CustomAggregate
annotation.
Determination of
$A$
Let
$I$
be the input set. If
$p$
is absent, let
$A=I$
with null values removed.
Otherwise, let
$q$
be the portion of
$p$
up to and including the last navigation property, if any, and any type-cast segment that immediately follows, and let
$r$
be the remainder, if any, of
$p$
that contains no navigation properties, such that
$p$
equals the concatenated path
$q⁄r$
. The aggregate transformation considers each entity reached via the path
$q$
exactly once. To this end, using the
$\Gamma$
notation
If
$q$
is non-empty, let
$E=\Gamma(I,q)$
and remove duplicates from that entity collection: If
multiple representations of the same non-transient entity
are reached, the service MUST merge them into one occurrence in
$E$
if they are complementary and MUST reject the request if they are contradictory. If
multiple occurrences of the same transient entity
are reached, the service MUST keep only one occurrence in
$E$
If
$q$
is empty, let
$E=I$
Then, if
$r$
is empty, let
$A=E$
, otherwise let
$A=\Gamma(E,r)$
, this consists of instances of structured types or primitive values, possibly with repetitions.
3.2.1.2 Keyword
as
Aggregate expressions can be followed by the
as
keyword followed by an
alias
Example 7:
GET /service/Sales?$apply=aggregate(Amount with sum as Total,
Amount with max as MxA)
results in
"@context"
"$metadata#Sales(Total, MxA)"
"value"
"Total@type"
"Decimal"
"Total"
24
"MxA@type"
"Decimal"
"MxA"
Example
GET /service/Sales?$apply=aggregate(Amount mul Product/TaxRate
with sum as Tax)
results in
"@context"
"$metadata#Sales(Tax)"
"value"
"Tax@type"
"Decimal"
"Tax"
2.08
An alias affects the structure of the output set: each alias corresponds to a dynamic property in a
$select
option.
3.2.1.3 Aggregation Methods
Values can be aggregated using the standard aggregation methods
sum
min
max
average
, and
countdistinct
, or with
custom aggregation methods
defined by the service. Only types 1 and 2 of the
aggregation algorithm
involve aggregation methods, and the algorithm ensures that no null values occur among the values to be aggregated.
3.2.1.3.1 Standard Aggregation Method
sum
The standard aggregation method
sum
can be applied to numeric values to return the sum of the values, or null if there are no values to be aggregated. The provider MUST choose a single type for the property across all instances of that type in the result that is capable of representing the aggregated values. This may require a larger integer type,
Edm.Decimal
with sufficient
Precision
and
Scale
, or
Edm.Double
Example 9:
GET /service/Sales?$apply=aggregate(Amount with sum as Total)
results in
"@context"
"$metadata#Sales(Total)"
"value"
"Total@type"
"Decimal"
"Total"
24
3.2.1.3.2 Standard Aggregation Method
min
The standard aggregation method
min
can be applied to values with a totally ordered domain to return the smallest of the values, or null if there are no values to be aggregated.
The result property will have the same type as the input property.
Example 10:
GET /service/Sales?$apply=aggregate(Amount with min as MinAmount)
results in
"@context"
"$metadata#Sales(MinAmount)"
"value"
"MinAmount@type"
"Decimal"
"MinAmount"
3.2.1.3.3 Standard Aggregation Method
max
The standard aggregation method
max
can be applied to values with a totally ordered domain to return the largest of the values, or null if there are no values to be aggregated.
The result property will have the same type as the input property.
Example 11:
GET /service/Sales?$apply=aggregate(Amount with max as MaxAmount)
results in
"@context"
"$metadata#Sales(MaxAmount)"
"value"
"MaxAmount@type"
"Decimal"
"MaxAmount"
3.2.1.3.4 Standard Aggregation Method
average
The standard aggregation method
average
can be applied to numeric values to return the sum of the values divided by the count of the values, or null if there are no values to be aggregated.
The provider MUST choose a single type for the property across all instances of that type in the result that is capable of representing the aggregated values; either
Edm.Double
or
Edm.Decimal
with sufficient
Precision
and
Scale
Example 12:
GET /service/Sales?$apply=aggregate(Amount with average as AverageAmount)
results in
"@context"
"$metadata#Sales(AverageAmount)"
"value"
"AverageAmount@type"
"Decimal"
"AverageAmount"
3.0
3.2.1.3.5 Standard Aggregation Method
countdistinct
The aggregation method
countdistinct
can be applied to arbitrary collections to count the distinct values. Instance comparison uses the definition of equality in
OData-URL, section 5.1.1.1.1
The result property MUST have type
Edm.Decimal
with
Scale
0 and sufficient
Precision
Example 13:
GET /service/Sales?$apply=aggregate(Product with countdistinct
as DistinctProducts)
results in
"@context"
"$metadata#Sales(DistinctProducts)"
"value"
"DistinctProducts@type"
"Decimal"
"DistinctProducts"
The number of instances in the input set can be counted with the
aggregate expression
$count
3.2.1.3.6 Custom Aggregation Methods
Services can define custom aggregation methods if the functionality offered by the standard aggregation methods is not sufficient for the intended consumers.
Custom aggregation methods MUST use a namespace-qualified name (see
OData-ABNF
), i.e. contain at least one dot. Dot-less names are reserved for future versions of this specification.
⚠ Example 14: custom aggregation method that concatenates distinct string values separated by commas
GET /service/Sales?$apply=groupby((Customer/Country),
aggregate(Amount with sum as Total,
Product/Name with Custom.concat as ProductNames))
results in
"@context"
"$metadata#Sales(Customer(Country),Total,ProductNames)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Total@type"
"Decimal"
"Total"
"ProductNames"
"Paper,Sugar"
"Customer"
"Country"
"USA"
},
"Total@type"
"Decimal"
"Total"
19
"ProductNames"
"Coffee,Paper,Sugar"
3.2.1.4 Aggregate Expression
$count
The aggregate expression
$count
is defined as type 3 in the
aggregation algorithm
. It MUST always specify an
alias
and MUST NOT specify an
aggregation method
The result property MUST have type
Edm.Decimal
with
Scale
0 and sufficient
Precision
Example 15:
GET /service/Sales?$apply=aggregate($count as SalesCount)
results in
"@context"
"$metadata#Sales(SalesCount)"
"value"
"SalesCount@type"
"Decimal"
"SalesCount"
3.2.2 Transformation
concat
The
concat
transformation takes two or more parameters, each of which is a sequence of set transformations.
It applies each transformation sequence to the input set and concatenates the intermediate output sets in the order of the parameters into the output set, preserving the ordering of the individual output sets as well as the structure of each instance in these sets, potentially leading to a non-homogeneously structured output set. If different intermediate output sets contain dynamic properties with the same alias, clients SHOULD ensure they have the same type and meaning in each intermediate output set.
⚠ Example 16:
GET /service/Sales?$apply=concat(topcount(2,Amount),
aggregate(Amount))
results in
"@context"
"$metadata#Sales(Amount)"
"value"
"ID"
"Amount"
"ID"
"Amount"
"Amount"
24
Note that two Sales entities with the second highest amount 4 exist in the input set; the entity with
ID
3 is included in the result, because the service chose to use the
ID
property for imposing a stable ordering.
3.2.3 Transformation
groupby
The
groupby
transformation takes one or two parameters where the second is a list of set transformations, separated by forward slashes to express that they are consecutively applied. If the second parameter is not specified, it defaults to a single transformation whose output set consists of a single instance of the
input type
without properties and without entity-id.
The
groupby
transformation partitions the input set by the values of certain “grouping properties” and applies the given set transformations to each partition, this is called “simple grouping”.
3.2.3.1 Simple Grouping
The first parameter of
groupby
specifies the
grouping properties
, a comma-separated parenthesized list
$G$
of one or more
data aggregation paths
with single-valued segments. The same path SHOULD NOT appear more than once; redundant property paths MAY be considered valid, but MUST NOT alter the meaning of the request. Navigation properties and stream properties specified in grouping properties are expanded by default (see
example 63
).
The algorithmic description of this transformation makes use of the following definitions: Let
$u[q]$
denote the value of a structural or navigation property
$q$
in an instance
$u$
. A path
$p_1$
is called a
prefix
of a path
$p$
if there is a non-empty path
$p_2$
such that
$p$
equals the concatenated path
$p_1/p_2$
. Let
$e$
denote the empty path.
The output set of the
groupby
transformation is constructed in five steps.
For each occurrence
$u$
in the input set, a projection is computed that contains only the grouping properties. This projection is
$s_G(u,e)$
and the function
$s_G(u,p)$
takes an instance and a path relative to the input set as arguments and is computed recursively as follows:
Let
$v$
be an instance of the type of
$u$
without properties and without entity-id.
For each structural or navigation property
$q$
of
$u$
If
$u$
has a subtype of the type addressed by
$p$
and
$q$
is only declared on that subtype, let
$p'=p/p''/q$
where
$p''$
is a type-cast to the subtype, otherwise let
$p'=p/q$
If
$p'$
occurs in
$G$
, let
$v[q]=u[q]$
Otherwise, if
$p'$
is a prefix of a path in
$G$
and
$u[q]$
has a structured type, let
$v[q]=s_G(u[q],p')$
Return
$v$
The input set is split into subsets where two instances are in the same subset if their projections are
the same
. If
representations of the same non-transient entity
are encountered during the comparison of two projections, the service MUST assign them to one subset with the merged representation if they are complementary and MUST reject the request if they are contradictory.
The set transformations from the second parameter are applied to each subset, resulting in a new set of potentially different structure and cardinality. Associated with each resulting set is the common projection of the instances in the subset from which the resulting set was computed.
Each set resulting from the previous step is transformed to contain the associated common projection
$s$
. This transformation is denoted by
$\Pi_G(s)$
and is defined below.
The output set is the concatenation of the transformed sets from the previous step. The order of occurrences from the same transformed set remains the same, and no order is defined between occurrences from different transformed sets.
Definition of
$\Pi_G(s)$
Prerequisites:
$G$
is a list of data aggregation paths and
$s$
is an instance of the
input type
The output set of the transformation
$\Pi_G(s)$
is in one-to-one correspondence with its input set via the
order-preserving
mapping
$u↦a_G(u,s,e)$
. The function
$a_G(u,s,p)$
takes two instances and a path relative to the input set as arguments and is computed recursively as follows:
If necessary, cast
$u$
to a subtype so that its type contains all structural and navigation properties of
$s$
For each structural or navigation property
$q$
of
$s$
If
$s$
has a subtype of the type addressed by
$p$
and
$q$
is only declared on that subtype, let
$p'=p/p''/q$
where
$p''$
is a type-cast to the subtype, otherwise let
$p'=p/q$
If
$q$
is a single-valued primitive structural property or
$p'$
occurs in
$G$
, let
$u[q]=s[q]$
. (In the case where
$p'$
occurs in
$G$
we also call
$q$
final segment from
$G$
.)
Otherwise, if
$q$
is single-valued, let
$u[q]=a_G(u[q],s[q],p')$
Otherwise, the behavior is undefined. (Such cases never occur when
$\Pi_G(s)$
is used in this document.)
Return
$u$
Example 17:
GET /service/Sales?$apply=groupby((Customer/Country,Product/Name),
aggregate(Amount with sum as Total))
results in
"@context"
"$metadata#Sales(Customer(Country),Product(Name),Total)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
If the second parameter is omitted, steps 2 and 3 above produce one instance containing only the grouping properties per distinct value combination.
⚠ Example 18:
GET /service/Sales?$apply=groupby((Product/Name,Amount))
results in
"@context"
"$metadata#Sales(Product(Name),Amount)"
"value"
"Product"
"Name"
"Coffee"
},
"Amount"
"Product"
"Name"
"Coffee"
},
"Amount"
"Product"
"Name"
"Paper"
},
"Amount"
"Product"
"Name"
"Paper"
},
"Amount"
"Product"
"Name"
"Paper"
},
"Amount"
"Product"
"Name"
"Sugar"
},
"Amount"
Note that the result has the same structure, but not the same content as
GET /service/Sales?$expand=Product($select=Name)&$select=Amount
groupby
transformation affects the structure of the output set similar to
$select
where each grouping property corresponds to an item in a
$select
clause.
3.3 Transformations Producing a Subset
These transformations produce an output set that is a subset of their input set, possibly in a different order. Some of the algorithmic descriptions below make use of the following definition: A total order of a collection is called
stable across requests
if it is the same for all requests that construct the collection by executing the same resource path and transformations, possibly nested, on the same underlying data.
⚠ Example 19: A stable total order is required for the input set of a
skip
transformation. The following request constructs that input set by executing the
groupby
transformation on the
Sales
entity collection, computing the total sales per customer. Because of the subsequent
skip
transformation, the service must endow this with a stable total order. Then the request divides the total sales per customer into pages of
$N$
customers and returns page number
$i$
in a reproducible manner (as long as the underlying data do not change).
GET /service/Sales?$apply=
groupby((Customer),aggregate(Amount with sum as Total))
/skip(M)/top(N)
where the number in
skip
is
$M=(i-1)⋅N$
. Other values of
$M$
can be used to skip, for example, half a page.
3.3.1 Top/bottom transformations
These transformations take two parameters. The first parameter MUST be an
expression
that is
evaluable on the input set as a collection
, without reference to an individual instance (and which therefore cannot be a property path). The second parameter MUST be an expression that is evaluated on each instance of the input set in turn.
The output set is constructed as follows:
Let
$A$
be a copy of the input set with a total order that is chosen by the service (it need not preserve any existing order). The total order MUST be stable across requests. (This is the order of the eventual output set of this transformation.)
Let
$B$
be a copy of
$A$
that is
stable-sorted
in ascending (for transformations starting with
bottom
) or descending (for transformations starting with
top
) order of the value specified in the second parameter. (This is the order in which contributions to the output set are considered.)
Start with an empty output set.
Loop over
$B$
in its total order.
Exit the loop if a condition is met. This condition depends on the transformation being executed and is given in the subsections below.
Insert the current item of the loop into the output set in the order of
$A$
Continue the loop.
For example, if the input set consists of non-transient entities and the datastore contains an index ordered by the second parameter and then the entity-id, a service may implement this algorithm with
$A=B$
ordered like this index.
The order of the output set can be influenced with a subsequent
orderby
transformation.
3.3.1.1 Transformations
bottomcount
and
topcount
The first parameter MUST evaluate to a positive integer
$c$
. The second parameter MUST evaluate to a primitive type whose values are totally ordered. In step 5, exit the loop if the cardinality of the output set equals
$c$
Example 20:
GET /service/Sales?$apply=bottomcount(2,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
Example 21:
GET /service/Sales?$apply=topcount(2,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
Note that two
Sales
entities with the second highest amount 4 exist in the input set; the entity with
ID
3 is included in the result, because the service chose to use the
ID
property for imposing a stable ordering in step 1. Such a logic needs to be in place even with a preceding
orderby
since it cannot be ensured that it creates a stable order of the instances on the expressions of the second parameter.
3.3.1.2 Transformations
bottompercent
and
toppercent
The first parameter MUST evaluate to a positive number
$p$
less than or equal to 100. The second parameter MUST evaluate to a number. In step 5, exit the loop if the ratio of the sum of the numbers addressed by the second parameter in the output set to their sum in the input set equals or exceeds
$p$
percent.
Example 22:
GET /service/Sales?$apply=bottompercent(50,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
Example 23:
GET /service/Sales?$apply=toppercent(50,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
3.3.1.3 Transformations
bottomsum
and
topsum
The first parameter MUST evaluate to a number
$s$
. The second parameter MUST be an
aggregatable expression
that evaluates to a number. In step 5, exit the loop if the sum of the numbers addressed by the second parameter in the output set is greater than or equal to
$s$
Example 24:
GET /service/Sales?$apply=bottomsum(7,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
Example 25:
GET /service/Sales?$apply=topsum(15,Amount)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
3.3.2 Transformation
filter
The
filter
transformation takes a Boolean expression that could also be passed as a
$filter
system query option. Its output set is the subset of the input set containing all instances (possibly with repetitions) for which this expression, evaluated relative to the instance, yields true. No order is defined on the output set.
Example 26:
GET /service/Sales?$apply=filter(Amount gt 3)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
"ID"
"Amount"
3.3.3 Transformation
orderby
The
orderby
transformation takes a list of expressions that could also be passed as a
$orderby
system query option. Its output set consists of the instances of the input set in the same order
$orderby
would produce for the given expressions, but keeping the relative order from the input set if the given expressions do not distinguish between two instances. The orderby transformation thereby performs a
stable-sort
. A service supporting this transformation MUST at least offer sorting by values addressed by property paths, including dynamic properties, with both suffixes
asc
and
desc
Example 27:
GET /service/Sales?$apply=groupby((Product/Name),
aggregate(Amount with sum as Total))
/orderby(Total desc)
results in
"@context"
"$metadata#Sales(Product(Name),Total)"
"value"
"Product"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
3.3.4 Transformation
The
transformation takes a search expression that could also be passed as a
$search
system query option. Its output set is the subset of the input set containing all instances (possibly with repetitions) that match this search expression. Closing parentheses in search expressions must be within single or double quotes in order to avoid syntax errors like
search())
. No order is defined on the output set.
Example 28: assuming that free-text search on
Sales
takes the related product name into account,
GET /service/Sales?$apply=search(coffee)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
3.3.5 Transformation
skip
The
skip
transformation takes a non-negative integer
$c$
as argument. Let
$A$
be a copy of the input set with a total order that extends any existing order of the input set but is otherwise chosen by the service. The total order MUST be stable across requests.
The transformation excludes from the output set the first
$c$
occurrences in
$A$
. It keeps all remaining instances in the same order as they occur in
$A$
Example 29:
GET /service/Sales?$apply=orderby(Customer/Name desc)/skip(2)/top(2)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
3.3.6 Transformation
top
The
top
transformation takes a non-negative integer
$c$
as argument. Let
$A$
be a copy of the input set with a total order that extends any existing order of the input set but is otherwise chosen by the service. The total order MUST be stable across requests.
If
$A$
contains more than
$c$
instances, the output set consists of the first
$c$
occurrences in
$A$
. Otherwise, the output set equals
$A$
. The instances in the output set are in the same order as they occur in
$A$
Note the transformation
top(0)
produces an empty output set.
Example 30:
GET /service/Sales?$apply=orderby(Customer/Name desc)/top(2)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
3.3.7 Stable Total Order Before
$skip
and
$top
When the system query options
$top
and
$skip
OData-Protocol, section 11.2.6.3
are executed after the system query option
$apply
and after
$filter
and
$orderby
, if applicable, they operate on a collection with a total order that extends any existing order but is otherwise chosen by the service. The total order MUST be stable across requests.
3.4 One-to-One Transformations
These transformations produce an output set in one-to-one correspondence with their input set. The output set is initially a clone of the input set, then dynamic properties are added to the output set. The values of properties copied from the input set are not changed, nor is the order of instances changed.
3.4.1 Transformation
identity
The output set of the
identity
transformation is its input set in unchanged order.
Example 31: Add a grand total row to the
Sales
result set
GET /service/Sales?$apply=concat(identity,aggregate(Amount with sum as Total))
3.4.2 Transformation
compute
The
compute
transformation takes a comma-separated list of one or more
compute expressions
as parameters.
A compute expression is a common expression followed by the
as
keyword, followed by an
alias
The output set is constructed by copying the instances of the input set and adding one dynamic property per compute expression to
each occurrence
in the output set. The name of each added dynamic property is the alias of the corresponding compute expression. The value of each added dynamic property is computed relative to the corresponding instance. Services MAY support expressions that address dynamic properties added by other expressions within the same
compute
transformation, provided that the service can determine an evaluation sequence. The type of the property is determined by the rules for evaluating common expressions and numeric promotion defined in
OData-URL, section 5.1.1
Example 32:
GET /service/Sales?$apply=compute(Amount mul Product/TaxRate as Tax)
results in
"@context"
"$metadata#Sales(*,Tax)"
"value"
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
14
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
12
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
24
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
48
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
56
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
12
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
14
"ID"
"Amount"
"Tax@type"
"Decimal"
"Tax"
28
3.5 Transformations Changing the Input Set Structure
The output set of the
join
transformations differs from their input set in the number of instances as well as in their structure, but reflects the order of the input set.
3.5.1 Transformations
join
and
outerjoin
The
join
and
outerjoin
transformations take as their first parameter
$p$
a collection-valued complex or navigation property, optionally followed by a type-cast segment to address only instances of that derived type or one of its sub-types, followed by the
as
keyword, followed by an
alias
. The optional second parameter specifies a transformation sequence
$T$
For each occurrence
$u$
in an
order-preserving loop
over the input set
the instance collection
$A$
addressed by
$p$
is identified.
If
$T$
is provided,
$A$
is replaced with the result of applying
$T$
to
$A$
In case of an
outerjoin
, if
$A$
is empty, a null instance is added to it.
For each occurrence
$v$
in an
order-preserving loop
over
$A$
an instance
$w$
is appended to the output set of the transformation:
The instance
$w$
is a clone of
$u$
with an additional dynamic property whose name is the given alias and whose value is
$v$
The dynamic property is a navigation property if
$p$
is a collection-valued navigation property, otherwise it is a complex property.
The dynamic property carries as control information the context URL of
$v$
Example 33: all links between products and sales instances
GET /service/Products?$apply=join(Sales as Sale)&$select=ID&$expand=Sale
results in
"@context"
"$metadata#Products(ID,Sale())"
"value"
"ID"
"P1"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P1"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P2"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P2"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P3"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P3"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P3"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
"ID"
"P3"
"Sale"
"@context"
"#Sales/$entity"
"ID"
"Amount"
In this example,
$expand=Sale
is used to include the target entities in the result. There are no subsequent transformations like
groupby
that would cause it to be expanded by default. If the first parameter
Sales
was a collection-valued complex property of type
SalesModel.SalesComplexType
, the complex property
Sale
would be in the result regardless, and its context would be
"@context": "#SalesModel.SalesComplexType"
Applying
outerjoin
instead would return an additional instance for product with
"ID": "P4"
and
Sale
having a null value.
3.6 Expressions Evaluable on a Collection
The following two subsections introduce two new types of
expression
that are evaluated relative to a collection, called the input collection.
These expressions are
either prepended with a collection-valued path
$p$
followed by a forward slash, like a lambda operator
OData-URL, section 5.1.1.13
. The collection identified by that path is then the input collection for the expression.
or prepended with the keyword
$these
followed by a forward slash, the input collection is then the
current collection
defined as follows:
In a system query option other than
$apply
, possibly nested within
$expand
or
$select
, the current collection is the collection that is the subject of the system query option.
In a path segment that addresses a subset of a collection
OData-URL, section 4.12
, the current collection is the collection that is the subject of the path segment.
In an
$apply
transformation, the current collection is the input set of the transformation.
3.6.1 Function
aggregate
The
aggregate
function allows the use of aggregated values in
expressions
. It takes a single parameter accepting an
aggregate expression
and returns the aggregated value of type
Edm.PrimitiveType
as the result from applying the aggregate expression on its input collection.
More precisely, if
$α$
is an aggregate expression, the function
$p/{\tt aggregate}(α)$
or
${\tt\$these}/{\tt aggregate}(α)$
evaluates to the value of the property
$D$
in the single instance of the output set that is produced when the transformation
${\tt aggregate}(α{\tt\ as\ }D)$
is applied with the input collection as input set.
Example 34: Sales making up at least a third of the total sales amount.
GET /service/Sales?$filter=Amount mul 3 ge $these/aggregate(Amount with sum)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"4"
"Amount"
Example 35: Products with more than 1.00 sales tax. The aggregate expression of type 2 combines paths with and without
$it
prefix (compare this with
example 8
).
GET /service/Products?$filter=Sales/aggregate(Amount mul $it/TaxRate with sum)
gt 1
⚠ Example 36: products with a single sale of at least twice the average sales amount
GET /service/Products?$filter=Sales/any(s:s/Amount ge
Sales/aggregate(Amount with average) mul 2)
Both examples result in
"@context"
"$metadata#Products"
"value"
"ID"
"P3"
"Name"
"Paper"
"Color"
"White"
"TaxRate"
14
3.6.2 Expression
$count
The expression
$count
evaluates to the cardinality of the input collection.
Example
37
: The input collection for
$count
consists of all sales entities, the top third of sales entities by amount form the result.
GET /service/Sales?$apply=topcount($these/$count div 3,Amount)
results in 2 (a third of 8, rounded down) entities. (This differs from
toppercent(33.3,Amount)
, which returns only the sales entity with
ID
4, because that already makes up a third of the total amount.)
"@context"
"$metadata#Sales"
"value"
"ID"
"Amount"
"ID"
"Amount"
A definition that is equivalent to a
$count
expression after a collection-valued path was made in
OData-URL, section 4.8
3.7 Function
isdefined
Properties that are not explicitly mentioned in
aggregate
or
groupby
are considered to have been
aggregated away
. Since they are treated as having the null value in
$filter
expressions
OData-URL, section 5.1.1.15
, the
$filter
expression
Product eq null
cannot distinguish between an instance containing the value for the null product and the instance containing the aggregated value across all products (where the
Product
has been aggregated away).
The function
isdefined
can be used to determine whether a property is present or absent in an instance. It takes a
single-valued property path
as its only parameter and returns true if the property is present in the instance for which the expression containing the
isdefined
function call is evaluated. A present property can still have the null value; it can represent a grouping of null values, or an aggregation that results in a null value.
Example 38:
Product
has been aggregated away, causing an empty result
GET /service/Sales?$apply=aggregate(Amount with sum as Total)
&$filter=isdefined(Product)
results in
"@context"
"$metadata#Sales(Total)"
"value"
[]
3.8 Evaluating
$apply
as an Expand and Select Option
The new system query option
$apply
can be used as an expand or select option to inline the result of aggregating related entities or nested instances. The rules for
evaluating
$apply
are applied in the context of the related collection of entities or the selected collection of instances, meaning this context defines the input set of the first transformation. Furthermore,
$apply
is evaluated first, and other expand or select options on the same (navigation) property are evaluated on the result of
$apply
Example 39: products with aggregated sales
GET /service/Products
?$expand=Sales($apply=aggregate(Amount with sum as Total))
results in
"@context"
"$metadata#Products(Sales(Total))"
"value"
"ID"
"P2"
"Name"
"Coffee"
"Color"
"Brown"
"TaxRate"
.06
"Sales"
"Total@type"
"Decimal"
"Total"
12
"ID"
"P3"
"Name"
"Paper"
"Color"
"White"
"TaxRate"
14
"Sales"
"Total@type"
"Decimal"
"Total"
"ID"
"P4"
"Name"
"Pencil"
"Color"
"Black"
"TaxRate"
14
"Sales"
"Total"
null
"ID"
"P1"
"Name"
"Sugar"
"Color"
"White"
"TaxRate"
.06
"Sales"
"Total@type"
"Decimal"
"Total"
3.9 ABNF for Extended URL Conventions
The normative ABNF construction rules for this specification are defined in
OData-Agg-ABNF
. They incrementally extend the rules defined in
OData-ABNF
4 Cross-Joins and Aggregation
OData supports querying related entities through defining navigation properties in the data model. These navigation paths help guide simple consumers in understanding and navigating relationships.
In some cases, however, requests need to span entity sets with no predefined associations. Such requests can be sent to the special resource
$crossjoin
instead of an individual entity set. The cross join of a list of entity sets is the Cartesian product of the listed entity sets, represented as a collection of complex type instances that have a navigation property with cardinality to-one for each participating entity set, and queries across entity sets can be formulated using these navigation properties. See
OData-URL, section 4.15
for details.
Where useful navigations exist it is beneficial to expose those as explicit navigation properties in the model, but the ability to pose queries that span entity sets not related by an association provides a mechanism for advanced consumers to use more flexible join conditions.
Example 40: if
Sale
had a string property
ProductID
instead of the navigation property
Product
, a “join” between
Sales
and
Products
could be accessed via the
$crossjoin
resource
GET /service/$crossjoin(Products,Sales)
?$expand=Products($select=Name),Sales($select=Amount)
&$filter=Products/ID eq Sales/ProductID
results in
"@context"
"$metadata#Collection(Edm.ComplexType)"
"value"
"Products"
"Name"
"Paper"
},
"Sales"
"Amount"
"Products"
"Name"
"Sugar"
},
"Sales"
"Amount"
Example 41: using the
$crossjoin
resource for aggregate queries
GET /service/$crossjoin(Products,Sales)
?$apply=filter(Products/ID eq Sales/ProductID)
/groupby((Products/Name),
aggregate(Sales/Amount with sum as Total))
results in
"@context"
"$metadata#Collection(Edm.ComplexType)"
"value"
"Products"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Products"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Products"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
The entity container may be annotated in the same way as entity sets to express which aggregate queries are supported, see
section 5
5 Vocabulary for Data Aggregation
The following terms are defined in the vocabulary for data aggregation
OData-VocAggr
5.1 Aggregation Capabilities
The term
ApplySupported
can be applied to an entity set, an entity type, or a collection if the target expression of the annotation starts with an entity container (see
example 43
). It describes the aggregation capabilities of the annotated target. If present, it implies that instances of the annotated target can contain dynamic properties as an effect of
$apply
even if they do not specify the
OpenType
attribute, see
OData-CSDL, section 6.3
. The term has a complex type with the following properties:
The
Transformations
collection lists all supported set transformations. Allowed values are the names of the standard transformations introduced in sections 3 and 6, and namespace-qualified names identifying a service-defined bindable function. If
Transformations
is omitted the server supports all transformations defined by this specification.
The
CustomAggregationMethods
collection lists supported custom aggregation methods. Allowed values are namespace-qualified names identifying service-specific aggregation methods. If omitted, no custom aggregation methods are supported.
Rollup
is reserved for later versions of this specifications. The functional scope of this version of the specification is expressed by giving
Rollup
the value
None
A non-empty
GroupableProperties
indicates that only the listed properties of the annotated target can be used in
groupby
A non-empty
AggregatableProperties
indicates that only the listed properties of the annotated target can be used in
aggregate
, optionally restricted to the specified aggregation methods.
All properties of
ApplySupported
are optional, so it can be used as a tagging annotation to signal unlimited support of aggregation.
The term
ApplySupportedDefaults
can be applied to an entity container. It allows to specify default support for aggregation capabilities
Transformations
CustomAggregationMethods
and
Rollup
that propagate to all collection-valued resources in the container. Annotating a specific collection-valued resource with the term
ApplySupported
overrides the default support with the specified properties using
PATCH
semantics:
Primitive or collection-valued properties specified in
ApplySupported
replace the corresponding properties specified in
ApplySupportedDefaults
Complex-valued properties specified in
ApplySupported
override the corresponding properties specified in ApplySupportedDefaults using
PATCH
semantics recursively.
Properties specified neither in
ApplySupported
nor in
ApplySupportedDefault
have their default value.
Example 42: an entity container with default support for everything defined in this specification
EntityContainer
Name=
"SalesData"
Annotation
Term=
"Aggregation.ApplySupportedDefaults"
/>
EntityContainer
Example
43
: Define aggregation support only for the products of a given category
Annotations
Target=
"SalesModel.SalesData/Categories/Products"
Annotation
Term=
"Aggregation.ApplySupported"
Annotation
Annotations
5.2 Custom Aggregates
The term
CustomAggregate
allows defining dynamic properties that can be used in
aggregate
. No assumptions can be made on how the values of these custom aggregates are calculated, whether they are null, and which input values are used.
When applied to an entity set, an entity type, or a collection if the target expression of the annotation starts with an entity container, the annotation specifies custom aggregates that are available for its instances and for aggregated instances resulting from these instances. When applied to an entity container, the annotation specifies custom aggregates whose input set may span multiple entity sets within the container.
A custom aggregate is identified by the value of the
Qualifier
attribute when applying the term. The value of the
Qualifier
attribute is the name of the dynamic property. The name MUST NOT collide with the names of other custom aggregates of the same model element.
The value of the annotation is a string with the qualified name of a primitive type or type definition in scope that specifies the type returned by the custom aggregate.
If the custom aggregate is associated with an entity set, entity type, or collection, the value of the
Qualifier
attribute MAY be identical to the name of a declared property of the instances in this set or collection. In these cases, the value of the annotation MUST have the same value as the
Type
attribute of the declared property. This is typically done when the custom aggregate is used as a default aggregate for that property. In this case the name refers to the custom aggregate within an aggregate expression without a
with
clause, and to the property in all other cases.
If the custom aggregate is associated with an entity container, the value of the
Qualifier
attribute MUST NOT collide with the names of any entity container children.
Example 44: Sales forecasts are modeled as a custom aggregate of the Sale entity type because it belongs there. For the budget, there is no appropriate structured type, so it is modeled as a custom aggregate of the
SalesData
entity container.
Annotations
Target=
"SalesModel.SalesData/Sales"
Annotation
Term=
"Aggregation.CustomAggregate"
Qualifier=
"Forecast"
String=
"Edm.Decimal"
/>
Annotations
Annotations
Target=
"SalesModel.SalesData"
Annotation
Term=
"Aggregation.CustomAggregate"
Qualifier=
"Budget"
String=
"Edm.Decimal"
/>
Annotations
These custom aggregates can be used in the
aggregate
transformation:
GET /service/Sales?$apply=groupby((Time/Month),aggregate(Forecast))
and:
GET /service/$crossjoin(Time)?$apply=groupby((Time/Year),aggregate(Budget))
5.3 Context-Defining Properties
Sometimes the value of a property or custom aggregate is only well-defined within the context given by values of other properties, e.g. a postal code together with its country, or a monetary amount together with its currency unit. These context-defining properties can be listed with the term
ContextDefiningProperties
whose type is a collection of property paths.
If present, the context-defining properties SHOULD be used as grouping properties when aggregating the annotated property or custom aggregate, or alternatively be restricted to a single value by a pre-filter operation. Services MAY respond with
400 Bad Request
if the context-defining properties are not sufficiently specified for calculating a meaningful aggregate value.
5.4 Annotation Example
Example 45: This simplified
Sales
entity set has a single aggregatable property
Amount
whose context is defined by the
Code
property of the related
Currency
, and a custom aggregate
Forecast
with the same context. The
Code
property of
Currencies
is groupable. All other properties are neither groupable nor aggregatable.
EntityType
Name=
"Currency"
Key
PropertyRef
Name=
"Code"
/>
Key
Property
Name=
"Code"
Type=
"Edm.String"
/>
Property
Name=
"Name"
Type=
"Edm.String"
Annotation
Term=
"Core.IsLanguageDependent"
/>
Property
EntityType
EntityType
Name=
"Sale"
Key
PropertyRef
Name=
"ID"
/>
Key
Property
Name=
"ID"
Type=
"Edm.String"
Nullable=
"false"
/>
Property
Name=
"Amount"
Type=
"Edm.Decimal"
Scale=
"variable"
Annotation
Term=
"Aggregation.ContextDefiningProperties"
Collection
PropertyPath
>Currency/CodePropertyPath
Collection
Annotation
Property
NavigationProperty
Name=
"Currency"
Type=
"SalesModel.Currency"
Nullable=
"false"
/>
EntityType
EntityContainer
Name=
"SalesData"
EntitySet
Name=
"Sales"
EntityType=
"SalesModel.Sale"
Annotation
Term=
"Aggregation.ApplySupported"
Record
PropertyValue
Property=
"AggregatableProperties"
Collection
Record
PropertyValue
Property=
"Property"
PropertyPath=
"Amount"
/>
Record
Collection
PropertyValue
PropertyValue
Property=
"GroupableProperties"
Collection
PropertyPath
>CurrencyPropertyPath
Collection
PropertyValue
Record
Annotation
Annotation
Term=
"Aggregation.CustomAggregate"
Qualifier=
"Forecast"
String=
"Edm.Decimal"
Annotation
Term=
"Aggregation.ContextDefiningProperties"
Collection
PropertyPath
>Currency/CodePropertyPath
Collection
Annotation
Annotation
EntitySet
EntitySet
Name=
"Currencies"
EntityType=
"SalesModel.Currency"
Annotation
Term=
"Aggregation.ApplySupported"
Record
PropertyValue
Property=
"GroupableProperties"
Collection
PropertyPath
>CodePropertyPath
Collection
PropertyValue
Record
Annotation
EntitySet
EntityContainer
5.5 Hierarchies
A hierarchy is an arrangement of entities whose values are represented as being “above”, “below”, or “at the same level as” one another.
🚧 Recursive hierarchies are defined in the following subsection. Any list of properties can be viewed as a leveled hierarchy with a fixed number of levels, for example, year, quarter and month, but this is not made explicit in the OData service.
5.5.1 Recursive Hierarchy
A recursive hierarchy is defined on a collection of entities by
determining which entities are part of the hierarchy and giving every such entity a single primitive non-null value that uniquely identifies it within the hierarchy. These entities are called
nodes
, and the primitive value is called the
node identifier
, and
associating with every node zero or more nodes from the same collection, called its
parent nodes
The recursive hierarchy is described in the model by an annotation of the entity type with the complex term
RecursiveHierarchy
with these properties:
The
NodeProperty
MUST be a path with single-valued segments ending in a primitive property. This property holds the node identifier of an entity that is a node in the hierarchy.
The
ParentNavigationProperty
MUST be a collection-valued or nullable single-valued navigation property path that addresses the entity type annotated with this term. It navigates from an entity that is a node in the hierarchy to its parent nodes.
The term
RecursiveHierarchy
can only be applied to entity types, and MUST be applied with a qualifier, which is used to reference the hierarchy in transformations operating on recursive hierarchies and in
hierarchy functions
. The same entity can serve as nodes in different recursive hierarchies, given different qualifiers.
root node
is a node without parent nodes. A recursive hierarchy can have one or more root nodes. A node is a
child node
of its parent nodes, a node without child nodes is a
leaf node
. Two nodes with a common parent node are
sibling nodes
and so are two root nodes.
The
descendants with maximum distance
$d≥1$
of a node are its child nodes and, if
$d>1$
, the descendants of these child nodes with maximum distance
$d-1$
. The
descendants
are the descendants with maximum distance
$d=∞$
. A node together with its descendants forms a
sub-hierarchy
of the hierarchy.
The
ancestors with maximum distance
$d≥1$
of a node are its parent nodes and, if
$d>1$
, the ancestors of these parent nodes with maximum distance
$d-1$
. The
ancestors
are the ancestors with maximum distance
$d=∞$
. The
ParentNavigationProperty
MUST be such that no node is an ancestor of itself, in other words: cycles are forbidden.
5.5.1.1 Hierarchy Functions
For testing the position of a given entity in a recursive hierarchy, the
Aggregation
vocabulary
OData-VocAggr
defines unbound functions. These have
a parameter pair
HierarchyNodes
HierarchyQualifier
where
HierarchyNodes
is a collection and
HierarchyQualifier
is the qualifier of a
RecursiveHierarchy
annotation on its common entity type. The node identifiers in this collection define the recursive hierarchy.
a parameter
Node
that contains the node identifier of the entity to be tested. Note that the test result depends only on this node identifier, not on any other property of the given entity
additional parameters, depending on the type of test (see below)
a Boolean return value for the outcome of the test.
The following functions are defined:
isnode
tests if the given entity is a node of the hierarchy.
isroot
tests if the given entity is a root node of the hierarchy.
isdescendant
tests if the given entity is a descendant with maximum distance
MaxDistance
of an ancestor node (whose node identifier is given in a parameter
Ancestor
), or equals the ancestor if
IncludeSelf
is true.
isancestor
tests if the given entity is an ancestor with maximum distance
MaxDistance
of a descendant node (whose node identifier is given in a parameter
Descendant
), or equals the descendant if
IncludeSelf
is true.
issibling
tests if the given entity and another entity (whose node identifier is given in a parameter
Other
) are sibling nodes.
isleaf
tests if the given entity is a leaf node.
5.5.2 Hierarchy Examples
The hierarchy terms can be applied to the
Example Data Model
⚠ Example 46: leveled hierarchies for products and time, and a recursive hierarchy for the sales organizations:
version=
"1.0"
encoding=
"UTF-8"
standalone=
"yes"
?>
edmx:Edmx
xmlns:edmx=
"http://docs.oasis-open.org/odata/ns/edmx"
Version=
"4.0"
edmx:Reference
Uri=
"https://docs.oasis-open.org/odata/odata-data-
aggregation-ext/v4.0/cs04/vocabularies/Org.OData.Aggregation.V1.xml"
edmx:Include
Alias=
"Aggregation"
Namespace=
"Org.OData.Aggregation.V1"
/>
edmx:Reference
edmx:DataServices
Schema
xmlns=
"http://docs.oasis-open.org/odata/ns/edm"
Alias=
"SalesModel"
Namespace=
"org.example.odata.salesservice"
Annotations
Target=
"SalesModel.SalesOrganization"
Annotation
Term=
"Aggregation.RecursiveHierarchy"
Qualifier=
"SalesOrgHierarchy"
Record
PropertyValue
Property=
"NodeProperty"
PropertyPath=
"ID"
/>
PropertyValue
Property=
"ParentNavigationProperty"
PropertyPath=
"Superordinate"
/>
Record
Annotation
Annotations
Schema
edmx:DataServices
edmx:Edmx
The recursive hierarchy
SalesOrgHierarchy
can be used in functions with the
$filter
system query option.
Example 47: requesting all organizations below EMEA
GET /service/SalesOrganizations?$filter=Aggregation.isdescendant(
HierarchyNodes=$root/SalesOrganizations,
HierarchyQualifier='SalesOrgHierarchy',
Node=ID,
Ancestor='EMEA')
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
"ID"
"Sales Netherlands"
"Name"
"Sales Netherlands"
"ID"
"Sales Germany"
"Name"
"Sales Germany"
"ID"
"EMEA South"
"Name"
"EMEA South"
"ID"
"EMEA North"
"Name"
"EMEA North"
Example 48: requesting just those organizations directly below EMEA
GET /service/SalesOrganizations?$filter=Aggregation.isdescendant(
HierarchyNodes=$root/SalesOrganizations,
HierarchyQualifier='SalesOrgHierarchy',
Node=ID,
Ancestor='EMEA',
MaxDistance=1)
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
"ID"
"EMEA South"
"Name"
"EMEA South"
"ID"
"EMEA North"
"Name"
"EMEA North"
Example 49: just the lowest-level organizations
GET /service/SalesOrganizations?$filter=Aggregation.isleaf(
HierarchyNodes=$root/SalesOrganizations,
HierarchyQualifier='SalesOrgHierarchy',
Node=ID)
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"Sales Office London"
"Name"
"Sales Office London"
"ID"
"Sales Office New York"
"Name"
"Sales Office New York"
Example 50: the lowest-level organizations including their superordinate’s
ID
GET /service/SalesOrganizations?$filter=Aggregation.isleaf(
HierarchyNodes=$root/SalesOrganizations,
HierarchyQualifier='SalesOrgHierarchy',
Node=ID)
&$expand=Superordinate($select=ID)
results in
"@context"
"$metadata#SalesOrganizations(*,Superordinate(ID))"
"value"
"ID"
"Sales Office London"
"Name"
"Sales Office London"
"Superordinate"
"ID"
"EMEA United Kingdom"
"ID"
"Sales Office New York"
"Name"
"Sales Office New York"
"Superordinate"
"ID"
"US East"
Example 51: the sales
ID
s involving sales organizations from EMEA
GET /service/Sales?$select=ID&$filter=Aggregation.isdescendant(
HierarchyNodes=$root/SalesOrganizations,
HierarchyQualifier='SalesOrgHierarchy',
Node=SalesOrganization/ID,
Ancestor='EMEA')
results in
"@context"
"$metadata#Sales(ID)"
"value"
"ID"
"ID"
"ID"
Further examples for recursive hierarchies using transformations operating on the hierarchy structure are provided in
section 7.9
5.6 Functions on Aggregated Entities
Service-defined bound functions that serve as set transformations MAY be annotated with the term
AvailableOnAggregates
to indicate that they are applicable to aggregated entities under specific conditions:
The
RequiredProperties
collection lists all properties that must be available in the aggregated entities; otherwise, the annotated function will be inapplicable.
Example 52: assume the product is an implicit input for a function bound to a collection of
Sales
, then aggregating away the product makes this function inapplicable.
6 Hierarchical Transformations
The transformations defined in this section are called hierarchical, because they make use of a recursive hierarchy and are defined in terms of hierarchy functions introduced in the previous section.
The transformations
ancestors
and
descendants
do not define an order on the output set. An order can be imposed by a subsequent
orderby
or
traverse
transformation or a
$orderby
. The output set of
traverse
is in preorder or postorder.
The algorithmic descriptions of the transformations make use of a
union
of collections, this is defined as an unordered collection containing the items from all these collections and from which duplicates have been removed.
The notation
$u[t]$
is used to denote the value of a property
$t$
, possibly preceded by a type-cast segment, in an instance
$u$
. It is also used to denote the value of a single-valued data aggregation path
$t$
, evaluated relative to
$u$
. The value of a collection-valued
data aggregation path
is denoted in the
$\Gamma$
notation
by
$γ(u,t)$
The notations introduced here are used throughout the following subsections.
6.1 Common Parameters for Hierarchical Transformations
The parameter lists defined in the following subsections have three mandatory parameters in common.
The recursive hierarchy is defined by a parameter pair
$(H,Q)$
, where
$H$
and
$Q$
MUST be specified as the first and second parameter. Here,
$H$
MUST be an expression of type
Collection(Edm.EntityType)
starting with
$root
that has no multiple occurrences of the same entity.
$H$
identifies the collection of node entities forming a recursive hierarchy based on an annotation of their common entity type with term
RecursiveHierarchy
with a
Qualifier
attribute whose value MUST be provided in
$Q$
. The property paths referenced by
NodeProperty
and
ParentNavigationProperty
in the
RecursiveHierarchy
annotation must be evaluable for the nodes in the recursive hierarchy, otherwise the service MUST reject the request. The
NodeProperty
is denoted by
$q$
in this section.
The third parameter MUST be a data aggregation path
$p$
with single- or collection-valued segments whose last segment MUST be a primitive property. The node identifier(s) of an instance
$u$
in the input set are the primitive values in
$γ(u,p)$
, they are reached via
$p$
starting from
$u$
. Let
$p=p_1/…/p_k/r$
with
$k≥0$
be the concatenation where each sub-path
$p_1,…,p_k$
consists of a collection-valued segment that is preceded by zero or more single-valued segments, and either
$r$
consists of one or more single-valued segments or
$k≥1$
and
${}/r$
is absent. Each segment can be prefixed with a type cast.
6.2 Hierarchical Transformations Producing a Subset
These transformations produce an output set that consists of certain instances from their input set, possibly with repetitions or in a different order.
6.2.1 Transformations
ancestors
and
descendants
In the simple case, the
ancestors
transformation takes an input set consisting of instances that belong to a recursive hierarchy
$(H,Q)$
. It determines a subset
$A$
of the input set and then determines the set of ancestors of
$A$
that were already contained in the input set. Its output set is the ancestors set, optionally including
$A$
In the more complex case, the instances in the input set are instead related to nodes in a recursive hierarchy. Then the
ancestors
transformation determines a subset
$A$
of the input set consisting of instances that are related to certain nodes in the hierarchy, called start nodes. The ancestors of these start nodes are then determined, and the output set consists of instances of the input set that are related to the ancestors, or optionally to the start nodes.
The
descendants
transformation works analogously, but with descendants.
$H$
$Q$
and
$p$
are the first three parameters defined
above
The fourth parameter is a transformation sequence
$T$
composed of transformations listed
section 3.3
or
section 6.2.1
and of service-defined bound functions whose output set is a subset of their input set.
$A$
is the output set of this sequence applied to the input set.
The fifth parameter
$d$
is optional and takes an integer greater than or equal to 1 that specifies the maximum distance between start nodes and ancestors or descendants to be considered. An optional final
keep start
parameter drives the optional inclusion of the subset or start nodes.
The output set of the transformation
${\tt ancestors}(H,Q,p,T,d,{\tt keep\ start})$
or
${\tt descendants}(H,Q,p,T,d,{\tt keep\ start})$
is defined as the
union
of the output sets of transformations
$F(u)$
applied to the input set for all
$u$
in
$A$
. For a given instance
$u$
, the transformation
$F(u)$
determines all instances of the input set whose node identifier is an ancestor or descendant of the node identifier of
$u$
If
$p$
contains only single-valued segments, then, for
ancestors
\[\matrix{
F(u)={\tt filter}(\hbox{\tt Aggregation.isancestor}(\hfill\\
\quad {\tt HierarchyNodes}=H,\;{\tt HierarchyQualifier}=\hbox{\tt{'$Q$'}},\hfill\\
\quad {\tt Node}=p,\;{\tt Descendant}=u[p],\;{\tt MaxDistance}=d,\;{\tt IncludeSelf}={\tt true}))\hfill
}\]
or, for
descendants
\[\matrix{
F(u)={\tt filter}(\hbox{\tt Aggregation.isdescendant}(\hfill\\
\quad {\tt HierarchyNodes}=H,\;{\tt HierarchyQualifier}=\hbox{\tt{'$Q$'}},\hfill\\
\quad {\tt Node}=p,\;{\tt Ancestor}=u[p],\;{\tt MaxDistance}=d,\;{\tt IncludeSelf}={\tt true})).\hfill
}\]
Otherwise
$p=p_1/…/p_k/r$
with
$k≥1$
, in this case the output set of the transformation
$F(u)$
is defined as the
union
of the output sets of transformations
$G(n)$
applied to the input set for all
$n$
in
$γ(u,p)$
. The output set of
$G(n)$
consists of the instances of the input set whose node identifier is an ancestor or descendant of the node identifier
$n$
For
ancestors
\[\matrix{
G(n)={\tt filter}(\hfill\\
\hskip1pc p_1/{\tt any}(y_1:\hfill\\
\hskip2pc y_1/p_2/{\tt any}(y_2:\hfill\\
\hskip3pc ⋱\hfill\\
\hskip4pc y_{k-1}/p_k/{\tt any}(y_k:\hfill\\
\hskip5pc \hbox{\tt Aggregation.isancestor}(\hfill\\
\hskip6pc {\tt HierarchyNodes}=H,\;{\tt HierarchyQualifier}=\hbox{\tt{'$Q$'}},\hfill\\
\hskip6pc {\tt Node}=y_k/r,\;{\tt Descendant}=n,\;{\tt MaxDistance}=d,\;{\tt IncludeSelf}={\tt true}\hfill\\
\hskip5pc )\hfill\\
\hskip4pc )\hfill\\
\hskip3pc ⋰\hfill\\
\hskip2pc )\hfill\\
\hskip1pc )\hfill\\
)\hfill
}\]
or, for
descendants
\[\matrix{
G(n)={\tt filter}(\hfill\\
\hskip1pc p_1/{\tt any}(y_1:\hfill\\
\hskip2pc y_1/p_2/{\tt any}(y_2:\hfill\\
\hskip3pc ⋱\hfill\\
\hskip4pc y_{k-1}/p_k/{\tt any}(y_k:\hfill\\
\hskip5pc \hbox{\tt Aggregation.isdescendant}(\hfill\\
\hskip6pc {\tt HierarchyNodes}=H,\;{\tt HierarchyQualifier}=\hbox{\tt{'$Q$'}},\hfill\\
\hskip6pc {\tt Node}=y_k/r,\;{\tt Ancestor}=n,\;{\tt MaxDistance}=d,\;{\tt IncludeSelf}={\tt true}\hfill\\
\hskip5pc )\hfill\\
\hskip4pc )\hfill\\
\hskip3pc ⋰\hfill\\
\hskip2pc )\hfill\\
\hskip1pc )\hfill\\
)\hfill
}\]
where
$y_1,…,y_k$
denote
lambdaVariableExpr
s as defined in
OData-ABNF
and
${}/r$
may be absent.
If parameter
$d$
is absent, the parameter
${\tt MaxDistance}=d$
is omitted. If
keep start
is absent, the parameter
${\tt IncludeSelf}={\tt true}$
is omitted.
Since the output set of
ancestors
is constructed as a union, no instance from the input set will occur more than once in it, even if, for example, a sale is related to both a sales organization and one of its ancestor organizations. For
descendants
, analogously.
Example 53: Request based on the
SalesOrgHierarchy
defined in
Hierarchy Examples
, with
Superordinate/$ref
expanded to illustrate the hierarchy relation
GET /service/SalesOrganizations?$apply=
ancestors($root/SalesOrganizations,SalesOrgHierarchy,ID,
filter(contains(Name,'East') or contains(Name,'Central')))
&$expand=Superordinate/$ref
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"EMEA"
"Name"
"EMEA"
"Superordinate"
"@id"
"SalesOrganizations('Sales')"
"ID"
"US"
"Name"
"US"
"Superordinate"
"@id"
"SalesOrganizations('Sales')"
"ID"
"Sales"
"Name"
"Sales"
"Superordinate"
null
Example 54: Request based on the
SalesOrgHierarchy
defined in
Hierarchy Examples
, with
Superordinate/$ref
expanded to illustrate the hierarchy relation
GET /service/SalesOrganizations?$apply=
descendants($root/SalesOrganizations,SalesOrgHierarchy,ID,
filter(Name eq 'US'),keep start)
&$expand=Superordinate/$ref
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"US West"
"Name"
"US West"
"Superordinate"
"@id"
"SalesOrganizations('US')"
"ID"
"US"
"Name"
"US"
"Superordinate"
"@id"
"SalesOrganizations('Sales')"
"ID"
"US East"
"Name"
"US East"
"Superordinate"
"@id"
"SalesOrganizations('US')"
⚠ Example 55: Input set and recursive hierarchy from two different entity sets
GET /service/Sales?$apply=
ancestors($root/SalesOrganizations,
SalesOrgHierarchy,
SalesOrganization/ID,
filter(contains(SalesOrganization/Name,'East')
or contains(SalesOrganization/Name,'Central')),
keep start)
results in
"@context"
"$metadata#Sales"
"value"
"ID"
"4"
"Amount"
"SalesOrganization"
"ID"
"US East"
"Name"
"US East"
"ID"
"5"
"Amount"
"SalesOrganization"
"ID"
"US East"
"Name"
"US East"
"ID"
"6"
"Amount"
"SalesOrganization"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
"ID"
"7"
"Amount"
"SalesOrganization"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
"ID"
"8"
"Amount"
"SalesOrganization"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
6.2.2 Transformation
traverse
The
traverse
transformation returns instances of the input set that are or are related to nodes of a given recursive hierarchy in a specified tree order.
🚧 This version of the specification defines the behavior of the
traverse
transformation only in recursive hierarchies where
RecursiveHierarchy/ParentNavigationProperty
is single-valued.
$H$
$Q$
and
$p$
are the first three parameters defined
above
The fourth parameter
$h$
of the
traverse
transformation is either
preorder
or
postorder
. Let
$H'$
be the collection of root nodes in the recursive hierarchy
$(H,Q)$
. Nodes in
$H'$
are called start nodes in this subsection (see
example 91
).
Let
$o$
be the list of all following parameters that are expressions which could also be passed as a
$orderby
system query option, if there are any. If
$o$
is present, the transformation
stable-sorts
$H'$
by
$o$
🚧 Future versions of this specification MAY allow an optional fifth parameter that comes before the parameter list
$o$
and could not be passed as a
$orderby
system query option.
The instances in the input set are related to one node (if
$p$
is single-valued) or multiple nodes (if
$p$
is collection-valued) in the recursive hierarchy. Given a node
$x$
, denote by
$\hat F(x)$
the collection of all instances in the input set that are related to
$x$
; these collections can overlap. For each
$u$
in
$\hat F(x)$
, the output set contains one instance that comprises the properties of
$u$
and additional properties that identify the node
$x$
. These additional properties are independent of
$u$
and are bundled into an instance called
$σ(x)$
. For example, if a sale
$u$
is related to two sales organizations and hence contained in both
$\hat F(x_1)$
and
$\hat F(x_2)$
, the output set will contain two instances
$(u,σ(x_1))$
and
$(u,σ(x_2))$
and
$σ(x_i)$
contributes a navigation property
SalesOrganization
A transformation
$F(x)$
is defined below such that
$\hat F(x)$
is the output set of
$F(x)$
applied to the input set of the
traverse
transformation.
Given a node
$x$
, the formulas below contain the transformation
$\Pi_G(σ(x))$
in order to inject the properties of
$σ(x)$
into the instances in
$\hat F(x)$
; this uses the function
$\Pi_G$
that is defined in the
simple grouping
section. Further,
$G$
is a list of
data aggregation paths
that shall be present in the output set, and
$σ$
is a function that maps each hierarchy node
$x$
to an instance of the
input type
containing the paths from
$G$
. As a consequence of the following definitions, only single-valued properties and “final segments from
$G$
” are nested into
$σ(x)$
, therefore the behavior of
$\Pi_G(σ(x))$
is well-defined.
The definition of
$σ(x)$
makes use of a function
$a(ε,t,x)$
, which returns a sparsely populated instance
$u$
in which only the path
$t$
has a value, namely
$u[t]=x$
Three cases are distinguished:
Case where the recursive hierarchy is defined on the input set
This case applies if the paths
$p$
and
$q$
are equal. Let
$σ(x)=x$
and let
$G$
be a list containing all structural and navigation properties of the entity type of
$H$
In this case
$\Pi_G(σ(x))$
injects all properties of
$x$
into the instances of the output set. (See
example 57
.)
Case where the recursive hierarchy is defined on the related entity type addressed by a navigation property path
This case applies if
$p'$
is a non-empty navigation property path and
$p''$
an optional type-cast segment such that
$p$
equals the concatenated path
$p'/p''/q$
. Let
$σ(x)=a(ε,p'/p'',x)$
and let
$G=(p')$
In this case
$\Pi_G(σ(x))$
injects the whole related entity
$x$
into the instances of the output set. The navigation property path
$p'$
is expanded by default. (See
example 58
.)
Case where the recursive hierarchy is related to the input set only through equality of node identifiers, not through navigation
If neither case 1 nor case 2 applies, let
$σ(x)=a(ε,p,x[q])$
and let
$G=(p)$
In this case
$\Pi_G(σ(x))$
injects only the node identifier of
$x$
into the instances of the output set.
Here paths are considered equal if their non-type-cast segments refer to the same model elements when evaluated relative to the input set (see
example 59
).
The function
$a(u,t,x)$
takes an instance, a path and another instance as arguments and is defined recursively as follows:
If
$u$
equals the special symbol
$ε$
, set
$u$
to a new instance of the
input type
without properties and without entity-id.
If
$t$
contains only one segment other than a type cast, let
$t_1=t$
, and let
$x'=x$
, then go to step 6.
Otherwise, let
$t_1$
be the first property segment in
$t$
, possibly together with a preceding type-cast segment, let
$t_2$
be any type-cast segment that immediately follows, and let
$t_3$
be the remainder such that
$t$
equals the concatenated path
$t_1/t_2/t_3$
where
${}/t_2$
may be absent.
Let
$u'$
be an instance of the type of
$t_1/t_2$
without properties and without entity-id.
Let
$x'=a(u',t_3,x)$
If
$t_1$
is single-valued, let
$u[t_1]=x'$
If
$t_1$
is collection-valued, let
$u[t_1]$
be a collection consisting of one item
$x'$
Return
$u$
(See
example 88
.)
Since start nodes are root nodes,
$σ(x)$
is computed exactly once for every node
$x$
, as part of the recursive formula for
$R(x)$
given below.
Let
$r_1,…,r_n$
be a sequence of the start nodes in
$H'$
preserving the order
of
$H'$
stable-sorted by
$o$
. Then the transformation
${\tt traverse}(H,Q,p,h,o)$
is defined as equivalent to
\[{\tt concat}(R(r_1),…,R(r_n)).\]
$R(x)$
is a transformation producing the specified tree order for a sub-hierarchy of
$H$
with root node
$x$
. Let
$c_1,…,c_m$
with
$m≥0$
be an
order-preserving sequence
of the
children
of
$x$
in
$(H,Q)$
. The
recursive formula for
$R(x)$
is as follows:
If
$h={\tt preorder}$
, then
\[R(x)={\tt concat}(F(x)/\Pi_G(σ(x)),R(c_1),…,R(c_m)).\]
If
$h={\tt postorder}$
, then
\[R(x)={\tt concat}(R(c_1),…,R(c_m),F(x)/\Pi_G(σ(x))).\]
The absence of cycles guarantees that the recursion terminates.
$F(x)$
is a transformation that determines for the specified node
$x$
the instances of the input set having the same node identifier as
$x$
If
$p$
contains only single-valued segments, then
\[F(x)={\tt filter}(p{\tt\ eq\ }x[q]).\]
Otherwise
$p=p_1/…/p_k/r$
with
$k≥1$
and
\[\matrix{
F(x)={\tt filter}(\hfill\\
\hskip1pc p_1/{\tt any}(y_1:\hfill\\
\hskip2pc y_1/p_2/{\tt any}(y_2:\hfill\\
\hskip3pc ⋱\hfill\\
\hskip4pc y_{k-1}/p_k/{\tt any}(y_k:\hfill\\
\hskip5pc y_k/r{\tt\ eq\ }x[q]\hfill\\
\hskip4pc )\hfill\\
\hskip3pc ⋰\hfill\\
\hskip2pc )\hfill\\
\hskip1pc )\hfill\\
)\hfill
}\]
where
$y_1,…,y_k$
denote
lambdaVariableExpr
s and
${}/r$
may be absent.
Example 56: Based on the
SalesOrgHierarchy
defined in
Hierarchy Examples
GET /service/SalesOrganizations?$apply=
descendants($root/SalesOrganizations,SalesOrgHierarchy,ID,
Name eq 'US',keep start)
/ancestors($root/SalesOrganizations,SalesOrgHierarchy,ID,
contains(Name,'East'),keep start)
/traverse($root/SalesOrganizations,SalesOrgHierarchy,ID,preorder)
&$expand=Superordinate/$ref
results in
"@context"
"$metadata#SalesOrganizations"
"value"
"ID"
"US"
"Name"
"US"
"Superordinate"
"@id"
"SalesOrganizations('Sales')"
"ID"
"US East"
"Name"
"US East"
"Superordinate"
"@id"
"SalesOrganizations('US')"
Example
57
: Postorder traversal of organizations in the hierarchy defined in
Hierarchy Examples
with
$p=q={\tt ID}$
(case 1 of the
definition
of
$σ(x)$
). In this case
$\Pi_G(σ(x))$
writes back the entire node into the output set of
$T$
GET /service/SalesOrganizations?$apply=
traverse($root/SalesOrganizations,SalesOrgHierarchy,ID,postorder)
&$select=ID,Name
&$expand=Superordinate($select=ID)
results in
"@context"
"$metadata#SalesOrganizations(ID,Name,Superordinate(ID))"
"value"
"ID"
"US West"
"Name"
"US West"
"Superordinate"
"ID"
"US"
"ID"
"US East"
"Name"
"US East"
"Superordinate"
"ID"
"US"
"ID"
"US"
"Name"
"US"
"Superordinate"
"ID"
"Sales"
"ID"
"EMEA Central"
"Name"
"EMEA Central"
"Superordinate"
"ID"
"EMEA"
"ID"
"EMEA"
"Name"
"EMEA"
"Superordinate"
"ID"
"Sales"
"ID"
"Sales"
"Name"
"Sales"
"Superordinate"
null
⚠ Example
58
: Postorder traversal of sales per organization in the hierarchy defined in
Hierarchy Examples
with
$p=p'/q={\tt SalesOrganization}/{\tt ID}$
and
$p'={\tt SalesOrganization}$
(case 2 of the
definition
of
$σ(x)$
).
GET /service/Sales?$apply=traverse(
$root/SalesOrganizations,
SalesOrgHierarchy,
SalesOrganization/ID,
postorder)
&$select=ID
&$expand=SalesOrganization($select=ID)
The result contains each sale once for every organization to which it belongs, directly or indirectly.
"@context"
"$metadata#Sales(ID,SalesOrganization(ID))"
"value"
"ID"
"SalesOrganization"
"ID"
"US West"
"ID"
"SalesOrganization"
"ID"
"US West"
"ID"
"SalesOrganization"
"ID"
"US West"
"ID"
"SalesOrganization"
"ID"
"US East"
"ID"
"SalesOrganization"
"ID"
"US East"
"ID"
"SalesOrganization"
"ID"
"US"
"ID"
"SalesOrganization"
"ID"
"US"
"ID"
"SalesOrganization"
"ID"
"US"
"ID"
"SalesOrganization"
"ID"
"US"
"ID"
"SalesOrganization"
"ID"
"US"
⚠ Example
59
: Although
$p={\tt ID}$
and
$q={\tt ID}$
, they are not equal in the sense of case 1, because they are evaluated relative to different entity sets. Hence, this is an example of case 3 of the
definition
of
$σ(x)$
, where no
Sales/ID
matches a
SalesOrganizations/ID
, that is, all
$F(x)$
have empty output sets.
GET /service/Sales?$apply=traverse(
$root/SalesOrganizations,
SalesOrgHierarchy,
ID,
postorder)
results in
"@context"
"$metadata#Sales(ID,SalesOrganization(ID))"
"value"
[]
7 Examples
The following examples show some common aggregation-related questions that can be answered by combining the transformations defined in
sections 3
and
7.1 Requesting Distinct Values
Grouping without specifying a set transformation returns the distinct combination of the grouping properties.
Example 60:
GET /service/Customers?$apply=groupby((Name))
results in
"@context"
"$metadata#Customers(Name)"
"value"
"Name"
"Luc"
"Name"
"Joe"
"Name"
"Sue"
Note that “Sue” appears only once although the customer base contains two different Sues.
Aggregation is also possible across related entities.
Example 61: customers that bought something
GET /service/Sales?$apply=groupby((Customer/Name))
results in
"@context"
"$metadata#Sales(Customer(Name))"
"value"
"Customer"
"Name"
"Joe"
"Customer"
"Name"
"Sue"
Since
groupby
expands navigation properties in grouping properties by default, this is the same result as if the request would include a
$expand=Customer($select=Name)
. The
groupby
removes all other properties.
Note that “Luc” does not appear in the aggregated result as he hasn’t bought anything and therefore there are no sales entities that refer/navigate to Luc.
However, even though both Sues bought products, only one “Sue” appears in the aggregate result. Including properties that guarantee the right level of uniqueness in the grouping can repair that.
Example 62:
GET /service/Sales?$apply=groupby((Customer/Name,Customer/ID))
results in
"@context"
"$metadata#Sales(Customer(Name,ID))"
"value"
"Customer"
"Name"
"Joe"
"ID"
"C1"
"Customer"
"Name"
"Sue"
"ID"
"C2"
"Customer"
"Name"
"Sue"
"ID"
"C3"
This could also have been formulated as
GET /service/Sales?$apply=groupby((Customer))
&$expand=Customer($select=Name,ID)
Example
63
: Grouping by navigation property
Customer
GET /service/Sales?$apply=groupby((Customer))
results in
"@context"
"$metadata#Sales(Customer())"
"value"
"Customer"
"ID"
"C1"
"Name"
"Joe"
"Country"
"USA"
"Customer"
"ID"
"C2"
"Name"
"Sue"
"Country"
"USA"
"Customer"
"ID"
"C3"
"Name"
"Sue"
"Country"
"Netherlands"
Example 64: the first question in the motivating example in
section 2.3
, which customers bought which products, can now be expressed as
GET /service/Sales?$apply=groupby((Customer/Name,Customer/ID,Product/Name))
and results in
"@context"
"$metadata#Sales(Customer(Name,ID),Product(Name))"
"value"
"Customer"
"Name"
"Joe"
"ID"
"C1"
},
"Product"
"Name"
"Coffee"
"Customer"
"Name"
"Joe"
"ID"
"C1"
},
"Product"
"Name"
"Paper"
"Customer"
"Name"
"Joe"
"ID"
"C1"
},
"Product"
"Name"
"Sugar"
"Customer"
"Name"
"Sue"
"ID"
"C2"
},
"Product"
"Name"
"Coffee"
"Customer"
"Name"
"Sue"
"ID"
"C2"
},
"Product"
"Name"
"Paper"
"Customer"
"Name"
"Sue"
"ID"
"C3"
},
"Product"
"Name"
"Paper"
"Customer"
"Name"
"Sue"
"ID"
"C3"
},
"Product"
"Name"
"Sugar"
⚠ Example
65
: grouping by properties of subtypes
GET /service/Products?$apply=groupby((SalesModel.FoodProduct/Rating,
SalesModel.NonFoodProduct/RatingClass))
results in
"@context"
"$metadata#Products(SalesModel.FoodProduct/Rating,
SalesModel.NonFoodProduct/RatingClass)"
"value"
"@type"
"#SalesModel.FoodProduct"
"Rating"
"@type"
"#SalesModel.FoodProduct"
"Rating"
null
"@type"
"#SalesModel.NonFoodProduct"
"RatingClass"
"average"
"@type"
"#SalesModel.NonFoodProduct"
"RatingClass"
null
⚠ Example
66
: grouping by a property of a subtype
GET /service/Products?$apply=groupby((SalesModel.FoodProduct/Rating))
results in a third group representing entities with no
SalesModel.FoodProduct/Rating
, including the
SalesModel.NonFoodProduct
s:
"@context"
"$metadata#Products(@Core.AnyStructure)"
"value"
"@type"
"#SalesModel.FoodProduct"
"Rating"
"@type"
"#SalesModel.FoodProduct"
"Rating"
null
7.2 Standard Aggregation Methods
The client may specify one of the predefined aggregation methods
min
max
sum
average
, and
countdistinct
, or a
custom aggregation method
, to aggregate an
aggregatable expression
. Expressions defining an aggregate method specify an
alias
. The aggregated values are returned in a dynamic property whose name is determined by the alias.
Example
67
GET /service/Products?$apply=groupby((Name),
aggregate(Sales/Amount with sum as Total))
results in
"@context"
"$metadata#Products(Name,Total)"
"value"
"Name"
"Coffee"
"Total@type"
"Decimal"
"Total"
12
"Name"
"Paper"
"Total@type"
"Decimal"
"Total"
"Name"
"Pencil"
"Total"
null
"Name"
"Sugar"
"Total@type"
"Decimal"
"Total"
Note that the base set of the request is
Products
, so there is a result item for product
Pencil
even though there are no sales items. The input set for the aggregation in the third row is
$I$
consisting of the pencil,
$p=q/r={\tt Sales}/{\tt Amount}$
$E=\Gamma(I,q)$
is empty and
$A=\Gamma(E,r)$
is also empty. The sum over the empty collection is null.
Example 68: Compute the aggregate as a property using the
aggregate
function in
$compute
GET /service/Products?$compute=Sales/aggregate(Amount with sum) as Total
results in
"@context"
"$metadata#Products(*,Total)"
"value"
"ID"
"P2"
"Name"
"Coffee"
"Color"
"Brown"
"TaxRate"
.06
"Total@type"
"Decimal"
"Total"
12
"ID"
"P3"
"Name"
"Paper"
"Color"
"White"
"TaxRate"
14
"Total@type"
"Decimal"
"Total"
"ID"
"P4"
"Name"
"Pencil"
"Color"
"Black"
"TaxRate"
14
"Total"
null
"ID"
"P1"
"Name"
"Sugar"
"Color"
"White"
"TaxRate"
.06
"Total@type"
"Decimal"
"Total"
Example 69: Alternatively,
join
could be applied to yield a flat structure:
GET /service/Products?$apply=
join(Sales as TotalSales,aggregate(Amount with sum as Total))
/groupby((Name,TotalSales/Total))
results in
"@context"
"$metadata#Products(Name,TotalSales())"
"value"
"Name"
"Coffee"
"TotalSales@context"
"#Sales(Total)/$entity"
"TotalSales"
"Total@type"
"Decimal"
"Total"
12
"Name"
"Paper"
"TotalSales@context"
"#Sales(Total)/$entity"
"TotalSales"
"Total@type"
"Decimal"
"Total"
"Name"
"Sugar"
"TotalSales@context"
"#Sales(Total)/$entity"
"TotalSales"
"Total@type"
"Decimal"
"Total"
Applying
outerjoin
instead would return an additional entity for product with
ID
“Pencil” and
TotalSales
having a null value.
Example 70:
GET /service/Sales?$apply=groupby((Customer/Country),
aggregate(Amount with average as AverageAmount))
results in
"@context"
"$metadata#Sales(Customer(Country),AverageAmount)"
"value"
"Customer"
"Country"
"Netherlands"
},
"AverageAmount"
1.6666666666666667
"Customer"
"Country"
"USA"
},
"AverageAmount"
3.8
Here the
AverageAmount
is of type
Edm.Double
Example 71:
$count
after navigation property
GET /service/Products?$apply=groupby((Name),
aggregate(Sales/$count as SalesCount))
results in
"@context"
"$metadata#Products(Name,SalesCount)"
"value"
"Name"
"Coffee"
"SalesCount@type"
"Decimal"
"SalesCount"
"Name"
"Paper"
"SalesCount@type"
"Decimal"
"SalesCount"
"Name"
"Pencil"
"SalesCount@type"
"Decimal"
"SalesCount"
"Name"
"Sugar"
"SalesCount@type"
"Decimal"
"SalesCount"
The
aggregate
function can not only be used in
$compute
but also in
$filter
and
$orderby
Example 72: Products with an aggregated sales volume of ten or more
GET /service/Products?$filter=Sales/aggregate(Amount with sum) ge 10
results in
"@context"
"$metadata#Products"
"value"
"ID"
"P2"
"Name"
"Coffee"
"Color"
"Brown"
"TaxRate"
.06
"ID"
"P3"
"Name"
"Paper"
"Color"
"White"
"TaxRate"
14
Example 73: Customers in descending order of their aggregated sales volume
GET /service/Customers?$orderby=Sales/aggregate(Amount with sum) desc
results in
"@context"
"$metadata#Customers"
"value"
"ID"
"C2"
"Name"
"Sue"
"Country"
"USA"
"ID"
"C1"
"Name"
"Joe"
"Country"
"USA"
"ID"
"C3"
"Name"
"Sue"
"Country"
"Netherlands"
"ID"
"C4"
"Name"
"Luc"
"Country"
"France"
Example 74: Contribution of each sales to grand total sales amount
GET /service/Sales?$compute=Amount divby $these/aggregate(Amount with sum)
as Contribution
results in
"@context"
"$metadata#Sales(*,Contribution)"
"value"
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
.0416666666666667
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
.0833333333333333
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
1666666666666667
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
3333333333333333
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
1666666666666667
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
.0833333333333333
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
.0416666666666667
"ID"
"Amount"
"Contribution@type"
"Decimal"
"Contribution"
.0833333333333333
Example 75: Product categories with at least one product having an aggregated sales amount greater than 10
GET /service/Categories?$filter=Products/any(
p:p/Sales/aggregate(Amount with sum) gt 10)
results in
"@context"
"$metadata#Categories"
"value"
"ID"
"PG1"
"Name"
"Food"
The
aggregate
function can also be applied inside
$apply
Example 76: Sales volume per customer in relation to total volume
GET /service/Sales?$apply=
groupby((Customer),aggregate(Amount with sum as CustomerAmount))
/compute(CustomerAmount divby $these/aggregate(CustomerAmount with sum)
as Contribution)
&$expand=Customer/$ref
results in
"@context"
"$metadata#Sales(Customer(),CustomerAmount,Contribution)"
"value"
"Customer"
"@id"
"Customers('C1')"
},
"Contribution@type"
"Decimal"
"Contribution"
2916667
"Customer"
"@id"
"Customers('C2')"
},
"Contribution@type"
"Decimal"
"Contribution"
"Customer"
"@id"
"Customers('C3')"
},
"Contribution@type"
"Decimal"
"Contribution"
2083333
7.3 Requesting Expanded Results
Example 77: use
outerjoin
to split up collection-valued navigation properties for grouping
GET /service/Customers?$apply=outerjoin(Sales as ProductSales)
/groupby((Country,ProductSales/Product/Name))
returns the different combinations of products sold per country:
"@context"
"$metadata#Customers(Country,ProductSales())"
"value"
"Country"
"Netherlands"
"ProductSales@context"
"#Sales(Product(Name))/$entity"
"ProductSales"
"Product"
"Name"
"Paper"
"Country"
"Netherlands"
"ProductSales@context"
"#Sales(Product(Name))/$entity"
"ProductSales"
"Product"
"Name"
"Sugar"
"Country"
"USA"
"ProductSales@context"
"#Sales(Product(Name))/$entity"
"ProductSales"
"Product"
"Name"
"Coffee"
"Country"
"USA"
"ProductSales@context"
"#Sales(Product(Name))/$entity"
"ProductSales"
"Product"
"Name"
"Paper"
"Country"
"USA"
"ProductSales@context"
"#Sales(Product(Name))/$entity"
"ProductSales"
"Product"
"Name"
"Sugar"
"Country"
"France"
"ProductSales"
null
7.4 Requesting Custom Aggregates
Custom aggregates are defined through the
CustomAggregate
annotation. They can be associated with an entity set, a collection or an entity container.
A custom aggregate can be used by specifying the name of the custom aggregate in the
aggregate
clause.
Example 78:
GET /service/Sales?$apply=groupby((Customer/Country),
aggregate(Amount with sum as Actual,Forecast))
results in
"@context"
"$metadata#Sales(Customer(Country),Actual,Forecast)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Actual@type"
"Decimal"
"Actual"
"Forecast@type"
"Decimal"
"Forecast"
"Customer"
"Country"
"USA"
},
"Actual@type"
"Decimal"
"Actual"
19
"Forecast@type"
"Decimal"
"Forecast"
21
When associated with an entity set a custom aggregate MAY have the same name as a property of the underlying entity type with the same type as the type returned by the custom aggregate. This is typically done when the aggregate is used as a default aggregate for that property.
Example 79: A custom aggregate can be defined with the same name as a property of the same type in order to define a default aggregate for that property.
GET /service/Sales?$apply=groupby((Customer/Country),aggregate(Amount))
results in
"@context"
"$metadata#Sales(Customer(Country),Amount)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Amount"
"Customer"
"Country"
"USA"
},
"Amount"
19
7.5 Aliasing
A property can be aggregated in multiple ways, each with a different alias.
Example 80:
GET /service/Sales?$apply=groupby((Customer/Country),
aggregate(Amount with sum as Total,
Amount with average as AvgAmt))
results in
"@context"
"$metadata#Sales(Customer(Country),Total,AvgAmt)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Total@type"
"Decimal"
"Total"
"AvgAmt@type"
"Decimal"
"AvgAmt"
1.6666667
"Customer"
"Country"
"USA"
},
"Total@type"
"Decimal"
"Total"
19
"AvgAmt@type"
"Decimal"
"AvgAmt"
3.8
There is no hard distinction between groupable and aggregatable properties: the same property can be aggregated and used to group the aggregated results.
Example 81:
GET /service/Sales?$apply=groupby((Amount),aggregate(Amount with sum as Total))
will return all distinct amounts appearing in sales orders and how much money was made with deals of this amount
"@context"
"$metadata#Sales(Amount,Total)"
"value"
"Amount"
"Total@type"
"Decimal"
"Total"
"Amount"
"Total@type"
"Decimal"
"Total"
"Amount"
"Total@type"
"Decimal"
"Total"
"Amount"
"Total@type"
"Decimal"
"Total"
7.6 Combining Transformations per Group
Dynamic property names may be reused in different transformation sequences passed to
concat
Example
82
: to get the best-selling product per country with sub-totals for every country, the partial results of a transformation sequence and a
groupby
transformation are concatenated:
GET /service/Sales?$apply=concat(
groupby((Customer/Country,Product/Name),
aggregate(Amount with sum as Total))
/groupby((Customer/Country),topcount(1,Total)),
groupby((Customer/Country),
aggregate(Amount with sum as Total)))
results in
"@context"
"$metadata#Sales(Customer(Country),Total)"
"value"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Total@type"
"Decimal"
"Total"
19
"Customer"
"Country"
"Netherlands"
},
"Total@type"
"Decimal"
"Total"
Example 83: transformation sequences are also useful inside
groupby
: Aggregate the amount by only considering the top two sales amounts per product and country:
GET /service/Sales?$apply=groupby((Customer/Country,Product/Name),
topcount(2,Amount)/aggregate(Amount with sum as Total))
results in
"@context"
"$metadata#Sales(Customer(Country),Product(Name),Total)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
Example
84
: concatenation of two different groupings “biggest sale per customer” and “biggest sale per product”, made distinguishable by a dynamic property:
GET /service/Sales?$apply=concat(
groupby((Customer),topcount(1,Amount))/compute('Customer' as per),
groupby((Product),topcount(1,Amount))/compute('Product' as per))
&$expand=Customer($select=ID),Product($select=ID)
In the result,
Sales
entities 4 and 6 occur twice each with contradictory values of the dynamic property
per
. If a UI consuming the response presents the two groupings in separate columns based on the
per
property, no contradiction effectively arises.
"@context"
"$metadata#Sales(*,per,Customer(ID),Product(ID))"
"value"
"Customer"
"ID"
"C1"
},
"Product"
"ID"
"P2"
},
"ID"
"3"
"Amount"
"per"
"Customer"
"Customer"
"ID"
"C2"
},
"Product"
"ID"
"P2"
},
"ID"
"4"
"Amount"
"per"
"Customer"
"Customer"
"ID"
"C3"
},
"Product"
"ID"
"P1"
},
"ID"
"6"
"Amount"
"per"
"Customer"
"Customer"
"ID"
"C3"
},
"Product"
"ID"
"P1"
},
"ID"
"6"
"Amount"
"per"
"Product"
"Customer"
"ID"
"C2"
},
"Product"
"ID"
"P2"
},
"ID"
"4"
"Amount"
"per"
"Product"
"Customer"
"ID"
"C2"
},
"Product"
"ID"
"P3"
},
"ID"
"5"
"Amount"
"per"
"Product"
7.7 Model Functions as Set Transformations
Example 85: As a variation of
example 82
, a query for returning the best-selling product per country and the total amount of the remaining products can be formulated with the help of a model function.
For this purpose, the model includes a definition of a
TopCountAndRemainder
function that accepts a count and a numeric property for the top entities:
edm:Function
Name=
"TopCountAndRemainder"
IsBound=
"true"
edm:Parameter
Name=
"EntityCollection"
Type=
"Collection(Edm.EntityType)"
/>
edm:Parameter
Name=
"Count"
Type=
"Edm.Int16"
/>
edm:Parameter
Name=
"Property"
Type=
"Edm.String"
/>
edm:ReturnType
Type=
"Collection(Edm.EntityType)"
/>
edm:Function
The function retains those entities that
topcount
also would retain, and replaces the remaining entities by a single aggregated entity, where only the numeric property has a value, which is the sum over those remaining entities:
GET /service/Sales?$apply=
groupby((Customer/Country,Product/Name),
aggregate(Amount with sum as Total))
/groupby((Customer/Country),
Self.TopCountAndRemainder(Count=1,Property='Total'))
results in
"@context"
"$metadata#Sales(Customer(Country),Total)"
"value"
"Customer"
"Country"
"Netherlands"
},
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"Netherlands"
},
"Total@type"
"Decimal"
"Total"
"Customer"
"Country"
"USA"
},
"Product"
"Name"
"Coffee"
},
"Total@type"
"Decimal"
"Total"
12
"Customer"
"Country"
"USA"
},
"Total@type"
"Decimal"
"Total"
Note that these two entities get their values for the Country property from the groupby transformation, which ensures that they contain all grouping properties with the correct values.
7.8 Controlling Aggregation per Rollup Level
For a leveled hierarchy, consumers may specify a different aggregation method per level as a hierarchy level below the root level.
Example 86: get the average of the overall amount by month per product.
Using a transformation sequence:
GET /service/Sales?$apply=groupby((Product/ID,Product/Name,Time/Month),
aggregate(Amount with sum) as Total))
/groupby((Product/ID,Product/Name),
aggregate(Total with average as MonthlyAverage))
7.9 Aggregation in Recursive Hierarchies
⚠ Example 87: The input set
Sales
is filtered along a hierarchy on a related entity (navigation property
SalesOrganization
) before an aggregation
GET /service/Sales?$apply=
descendants($root/SalesOrganizations,
SalesOrgHierarchy,
SalesOrganization/ID,
filter(SalesOrganization/Name eq 'US'),
keep start)
/aggregate(Amount with sum as TotalAmount)
The same aggregate value is computed if the input set is the hierarchical entity
SalesOrganizations
and an assumed partner navigation property
Sales
of
SalesOrganization
appears in the
aggregate
transformation
GET /service/SalesOrganizations?$apply=
descendants($root/SalesOrganizations,
SalesOrgHierarchy,
ID,
filter(Name eq 'US'),
keep start)
/aggregate(Sales/Amount with sum as TotalAmount)
Example
88
: Preorder traversal of a hierarchy with 1:N relationship with collection-valued segment
$p_1={\tt Sales}$
and
$r={\tt SalesOrganization}/{\tt ID}$
GET /service/Products?$apply=traverse(
$root/SalesOrganizations,
SalesOrgHierarchy,
Sales/SalesOrganization/ID,
preorder,
Name asc)
&$select=ID
The result contains multiple instances of the same
Product
that differ in their
Sales
navigation property even though they agree in their
ID
key property. The node
$x$
with
$x/{\tt ID}={}$
"US"
has
$σ(x)={}$
{"Sales": [{"SalesOrganization": {"ID": "US"}}]}
"@context"
"$metadata#Products(ID,Sales(SalesOrganization(ID)))"
"value"
"ID"
"P1"
"Sales"
"SalesOrganization"
"ID"
"Sales"
"ID"
"P2"
"Sales"
"SalesOrganization"
"ID"
"Sales"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"Sales"
"ID"
"P1"
"Sales"
"SalesOrganization"
"ID"
"EMEA"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"EMEA"
"ID"
"P1"
"Sales"
"SalesOrganization"
"ID"
"EMEA Central"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"EMEA Central"
"ID"
"P1"
"Sales"
"SalesOrganization"
"ID"
"US"
"ID"
"P2"
"Sales"
"SalesOrganization"
"ID"
"US"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"US"
"ID"
"P2"
"Sales"
"SalesOrganization"
"ID"
"US East"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"US East"
"ID"
"P1"
"Sales"
"SalesOrganization"
"ID"
"US West"
"ID"
"P2"
"Sales"
"SalesOrganization"
"ID"
"US West"
"ID"
"P3"
"Sales"
"SalesOrganization"
"ID"
"US West"
7.10 Maintaining Recursive Hierarchies
Besides changes to the structural properties of the entities in a hierarchical collection, hierarchy maintenance involves changes to the parent-child relationships.
Example 89: Move a sales organization Switzerland under the parent EMEA Central by binding the parent navigation property to EMEA Central
OData-JSON, section 8.5
PATCH
/service/SalesOrganizations('Switzerland')
Content-Type:
application/json
"Superordinate"
"@id"
"SalesOrganizations('EMEA Central')"
results in
204 No Content
Deleting the parent from the sales organization Switzerland (making it a root) can be achieved either with:
PATCH
/service/SalesOrganizations('Switzerland')
Content-Type:
application/json
"Superordinate"
"@id"
null
or with:
DELETE /service/SalesOrganizations('Switzerland')/Superordinate/$ref
Example
90
: If the parent navigation property contained a referential constraint for the key of the target
OData-CSDL, section 8.5
EntityType
Name=
"SalesOrganization"
Key
PropertyRef
Name=
"ID"
/>
Key
Property
Name=
"ID"
Type=
"Edm.String"
Nullable=
"false"
/>
Property
Name=
"Name"
Type=
"Edm.String"
/>
Property
Name=
"SuperordinateID"
Type=
"Edm.String"
/>
NavigationProperty
Name=
"Superordinate"
Type=
"SalesModel.SalesOrganization"
ReferentialConstraint
Property=
"SuperordinateID"
ReferencedProperty=
"ID"
/>
NavigationProperty
EntityType
then alternatively the property taking part in the referential constraint
OData-Protocol, section 11.4.8.1
could be changed to EMEA Central:
PATCH
/service/SalesOrganizations('Switzerland')
Content-Type:
application/json
"SuperordinateID"
"EMEA Central"
If the parent-child relationship between sales organizations is maintained in a separate entity set, a node can have multiple parents, with additional information on each parent-child relationship.
⚠ Example
91
: Assume the relation from a node to its parent nodes contains a weight:
EntityType
Name=
"SalesOrganizationRelation"
Key
PropertyRef
Name=
"Superordinate/ID"
Alias=
"SuperordinateID"
/>
Key
Property
Name=
"Weight"
Type=
"Edm.Decimal"
Nullable=
"false"
DefaultValue=
"1"
/>
NavigationProperty
Name=
"Superordinate"
Type=
"SalesModel.SalesOrganization"
Nullable=
"false"
/>
EntityType
EntityType
Name=
"SalesOrganization"
Key
PropertyRef
Name=
"ID"
/>
Key
Property
Name=
"ID"
Type=
"Edm.String"
Nullable=
"false"
/>
Property
Name=
"Name"
Type=
"Edm.String"
/>
NavigationProperty
Name=
"Relations"
Type=
"Collection(SalesModel.SalesOrganizationRelation)"
Nullable=
"false"
ContainsTarget=
"true"
/>
Annotation
Term=
"Aggregation.RecursiveHierarchy"
Qualifier=
"MultiParentHierarchy"
Record
PropertyValue
Property=
"NodeProperty"
PropertyPath=
"ID"
/>
PropertyValue
Property=
"ParentNavigationProperty"
NavigationPropertyPath=
"Relations/Superordinate"
/>
Record
Annotation
EntityType
Further assume the following relationships between sales organizations:
ID
Relations/SuperordinateID
Relations/Weight
US
Sales
EMEA
Sales
EMEA Central
EMEA
Atlantis
US
0.6
Atlantis
EMEA
0.4
Phobos
Mars
Then Atlantis is a node with two parents. The standard hierarchical transformations
ancestors
and
descendants
disregard the weight property and consider both parents equally valid. Transformation
traverse
has no defined behavior.
Since this example contains no referential constraint, there is no analogy to
example 90
. The alias
SuperordinateID
cannot be used in the payload, the following request is invalid:
POST
/service/SalesOrganizations('Mars')/Relations
Content-Type:
application/json
"SuperordinateID"
"Sales"
The alias
SuperordinateID
is used in the request to delete the added relationship again:
DELETE /service/SalesOrganizations('Mars')/Relations('Sales')
7.11 Transformation Sequences
Applying aggregation first covers the most prominent use cases. The slightly more sophisticated question “how much money is earned with small sales” requires filtering the base set before applying the aggregation. To enable this type of question several transformations can be specified in
$apply
in the order they are to be applied, separated by a forward slash.
Example 92:
GET /service/Sales?$apply=filter(Amount le 1)
/aggregate(Amount with sum as Total)
means “filter first, then aggregate”, and results in
"@context"
"$metadata#Sales(Total)"
"value"
"Total@type"
"Decimal"
"Total"
Using
filter
within
$apply
does not preclude using it as a normal system query option.
Example 93:
GET /service/Sales?$apply=filter(Amount le 2)/groupby((Product/Name),
aggregate(Amount with sum as Total))
&$filter=Total ge 4
results in
"@context"
"$metadata#Sales(Product(Name),Total)"
"value"
"Product"
"Name"
"Paper"
},
"Total@type"
"Decimal"
"Total"
"Product"
"Name"
"Sugar"
},
"Total@type"
"Decimal"
"Total"
For further examples, consider another data model containing entity sets for cities, countries and continents and the obvious associations between them.
Example 94: getting the population per country with
GET /service/Cities?$apply=groupby((Continent/Name,Country/Name),
aggregate(Population with sum as TotalPopulation))
results in
"@context"
"$metadata#Cities(Continent(Name),Country(Name),
TotalPopulation)"
"value"
"Continent"
"Name"
"Asia"
},
"Country"
"Name"
"China"
},
"TotalPopulation@type"
"Int32"
"TotalPopulation"
1412000000
"Continent"
"Name"
"Asia"
},
"Country"
"Name"
"India"
},
"TotalPopulation@type"
"Int32"
"TotalPopulation"
1408000000
Example 95: all countries with megacities and their continents
GET /service/Cities?$apply=filter(Population ge 10000000)
/groupby((Continent/Name,Country/Name),
aggregate(Population with sum as TotalPopulation))
Example 96: all countries with tens of millions of city dwellers and the continents only for these countries
GET /service/Cities?$apply=groupby((Continent/Name,Country/Name),
aggregate(Population with sum as CountryPopulation))
/filter(CountryPopulation ge 10000000)
/concat(identity,
groupby((Continent/Name),
aggregate(CountryPopulation with sum
as TotalPopulation)))
or
GET /service/Cities?$apply=groupby((Continent/Name,Country/Name),
aggregate(Population with sum as CountryPopulation))
/filter(CountryPopulation ge 10000000)
/concat(groupby((Continent/Name,Country/Name),
aggregate(CountryPopulation with sum
as TotalPopulation)),
groupby((Continent/Name),
aggregate(CountryPopulation with sum
as TotalPopulation)))
Example 97: all countries with tens of millions of city dwellers and all continents with cities independent of their size
GET /service/Cities?$apply=groupby((Continent/Name,Country/Name),
aggregate(Population with sum as CountryPopulation))
/concat(filter(CountryPopulation ge 10000000),
groupby((Continent/Name),
aggregate(CountryPopulation with sum
as TotalPopulation)))
Example 98: assuming that
Amount
is a custom aggregate in addition to the property, determine the total for countries with an
Amount
greater than 1000
GET /service/SalesOrders?$apply=
groupby((Customer/Country),aggregate(Amount))
/filter(Amount gt 1000)
/aggregate(Amount)
8 Conformance
Conforming services MUST follow all rules of this specification for the set transformations and aggregation methods they support. They MUST implement all set transformations and aggregation methods they advertise via the annotation
ApplySupported
Conforming clients MUST be prepared to consume a model that uses any or all of the constructs defined in this specification, including custom aggregation methods defined by the service, and MUST ignore any constructs not defined in this version of the specification.
Appendix A. References
This appendix contains the normative references that are used in this document.
While any hyperlinks included in this appendix were valid at the time of publication, OASIS cannot guarantee their long-term validity.
A.1 Normative References
The following documents are referenced in such a way that some or all of their content constitutes requirements of this document.
OData-ABNF
ABNF components: OData ABNF Construction Rules Version 4.01 and OData ABNF Test Cases.
See link in “
Related work
” section on cover page.
OData-Agg-ABNF
OData Aggregation ABNF Construction Rules Version 4.0.
See link in “
Additional artifacts
” section on cover page.
OData-CSDL
OData Common Schema Definition Language (CSDL) JSON Representation Version 4.01.
See link in “
Related work
” section on cover page.
OData Common Schema Definition Language (CSDL) XML Representation Version 4.01.
See link in “
Related work
” section on cover page.
OData-JSON
OData JSON Format Version 4.01.
See link in “
Related work
” section on cover page.
OData-Protocol
OData Version 4.01. Part 1: Protocol.
See link in “
Related work
” section on cover page.
OData-URL
OData Version 4.01. Part 2: URL Conventions.
See link in “
Related work
” section on cover page.
OData-VocAggr
OData Aggregation Vocabulary.
See link in “
Additional artifacts
” section on cover page.
OData-VocCore
OData Core Vocabulary.
See link in “
Related work
” section on cover page.
RFC2119
Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997
RFC8174
Leiba, B., “Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words”, BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017
Appendix B. Acknowledgments
B.1 Special Thanks
The contributions of the OASIS OData Technical Committee members, enumerated in
OData-Protocol, section C.2
, are gratefully acknowledged.
B.2 Participants
OData TC Members:
First Name
Last Name
Company
George
Ericson
Dell
Hubert
Heijkers
IBM
Ling
Jin
IBM
Stefan
Hagen
Individual
Michael
Pizzo
Microsoft
Christof
Sprenger
Microsoft
Ralf
Handl
SAP SE
Gerald
Krause
SAP SE
Heiko
Theißen
SAP SE
Martin
Zurmuehl
SAP SE
Appendix C. Revision History
Revision
Date
Editor
Changes Made
Working Draft 01
2012-11-12
Ralf Handl
Translated contribution into OASIS format
Committee Specification Draft 01
2013-07-25
Ralf Handl
Hubert Heijkers
Gerald Krause
Michael Pizzo
Martin Zurmuehl
Switched to pipe-and-filter-style query language based on composable set transformations
Fleshed out examples and addressed numerous editorial and technical issues processed through the TC
Added Conformance section
Committee Specification Draft 02
2014-01-09
Ralf Handl
Hubert Heijkers
Gerald Krause
Michael Pizzo
Martin Zurmuehl
Dynamic properties used all aggregated values either via aliases or via custom aggregates
Refactored annotations
Committee Specification Draft 03
2015-07-16
Ralf Handl
Hubert Heijkers
Gerald Krause
Michael Pizzo
Martin Zurmuehl
Added compute transformation
Minor clean-up
Committee Specification Draft 04
2023-07-05
Ralf Handl
Hubert Heijkers
Gerald Krause
Michael Pizzo
Heiko Theißen
Added section about fundamentals of input and output sets
Algorithmic descriptions of transformations
Added join and outerjoin transformations, replaced expand by addnested
Added transformations orderby, skip, top, nest
Added transformations for recursive hierarchies, updated related filter functions
Added functions evaluable on a collection, introduced keyword $these
Merged section 4 “Representation of Aggregated Instances” into section 3
Remove actions and functions (except set transformations) on aggregated entities, adapted section “Actions and Functions on Aggregated Entities”
Committee Specification 03
2023-09-19
Ralf Handl
Gerald Krause
Heiko Theißen
Non-material changes from public review feedback
Committee Specification Draft 05
2025-10-01
Gerald Krause
Heiko Theißen
Remove sections not intended for OASIS Standard
Committee Specification 04
2025-11-18
Gerald Krause
Heiko Theißen
No changes from public review
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