/sap-abap-cds

ABAP CDS Associations Reference

Complete reference for defining and using associations in ABAP CDS views.

Source: https://help.sap.com/doc/abapdocu_752_index_htm/7.52/en-us/abencds_f1_association.htm

Version Note: Associations with explicit join type (INNER, LEFT OUTER) are available from 7.40 SP08. New cardinality syntax (association to one/to many) requires 7.57+ / S/4HANA Cloud Release 2302+. On 7.40, use bracket notation [0..1], [1..*].

What Are Associations?

Associations define relationships between CDS entities. Unlike joins, associations are join-on-demand - the actual database join only occurs when fields from the associated entity are accessed.

Key Benefits:

• Lazy evaluation improves performance
• Cleaner data model representation
• Reusable relationship definitions
• Support for navigation in OData and RAP

Association Syntax

Basic Definition

define view Z_EXAMPLE as select from source_table as s
  association [cardinality] to target_entity as _Alias
    on condition
{
  key s.key_field,
      s.field1,

      // Expose association
      _Alias
}

Naming Convention

SAP recommends prefixing association aliases with underscore:

• _Customer
• _Items
• _Currency

This distinguishes associations from regular fields.

Cardinality

Cardinality Notation

New Cardinality Syntax (Release 2302+)

association to one _Target on ...      -- Equivalent to [0..1]
association to many _Targets on ...    -- Equivalent to [0..*]

Compatibility Note: This simplified syntax is available in SAP S/4HANA Cloud 2302+ and SAP NetWeaver ABAP 7.57+. Earlier releases require the bracketed cardinality notation [0..1], [0..*], etc.

Cardinality Examples

-- Optional single record (e.g., customer details)
association [0..1] to customer_details as _Details
  on $projection.kunnr = _Details.kunnr

-- Required single record (e.g., company code)
association [1..1] to t001 as _Company
  on $projection.bukrs = _Company.bukrs

-- Multiple records (e.g., order items)
association [0..*] to order_items as _Items
  on $projection.vbeln = _Items.vbeln

-- At least one record expected
association [1..*] to spfli as _Flights
  on $projection.carrid = _Flights.carrid

Join Condition

Using $projection

Reference fields from the current view's projection:

association [0..1] to makt as _Text
  on $projection.matnr = _Text.matnr
 and $projection.spras = _Text.spras

Using Source Alias

Reference fields from the source table directly:

define view Z_EXAMPLE as select from mara as m
  association [0..1] to makt as _Text
    on m.matnr = _Text.matnr

Complex Conditions

association [0..*] to price_conditions as _Prices
  on $projection.matnr = _Prices.matnr
 and $projection.vkorg = _Prices.vkorg
 and _Prices.valid_from <= $session.system_date
 and _Prices.valid_to >= $session.system_date

Exposing Associations

Direct Exposure

Makes association available to consumers:

{
  key field1,
      field2,

      // Expose entire association
      _Customer,
      _Items
}

Redirected Association

Redirect to a different target:

_Customer : redirected to Z_CUSTOMER_VIEW

Filtered Association

Expose with additional filter:

_Items[Status = 'ACTIVE'] as _ActiveItems

Using Associations

Ad-hoc Field Access

Access individual fields (triggers join):

{
  key vbeln,
      _Customer.name1 as CustomerName,
      _Customer.ort01 as CustomerCity
}

Path Expressions

Navigate through associations:

_Header._Customer.name1 as CustomerName

Path Filter with Cardinality Indicator

When filtering reduces a to-many association to single record:

_Items[1: ItemNumber = '000010'].Material as FirstItemMaterial

The 1: indicates the filter results in a single record.

Association vs Join Comparison

When to Use Associations

Performance Difference

Association (Join-on-Demand):

define view Z_WITH_ASSOC as select from vbak
  association [0..1] to kna1 as _Customer
    on $projection.kunnr = _Customer.kunnr
{
  key vbeln,
      kunnr,
      _Customer  -- Join NOT executed yet
}

-- ABAP: SELECT vbeln, kunnr FROM z_with_assoc
-- Only 2 fields selected, no join needed

Join (Always Executed):

define view Z_WITH_JOIN as select from vbak as v
  left outer join kna1 as c on v.kunnr = c.kunnr
{
  key v.vbeln,
      v.kunnr,
      c.name1   -- Join ALWAYS executed
}

-- ABAP: SELECT vbeln, kunnr FROM z_with_join
-- Join executed even if name1 not needed

Default Association

Create association to same entity type for self-reference:

define view Z_HIERARCHY as select from org_unit as o
  association [0..1] to Z_HIERARCHY as _Parent
    on $projection.parent_id = _Parent.org_unit_id
{
  key org_unit_id,
      parent_id,
      name,
      _Parent
}

Propagated Associations

Associations from underlying views are automatically propagated:

-- Base view
define view Z_BASE as select from mara
  association [0..1] to makt as _Text on ...
{
  key matnr,
      _Text
}

-- Consuming view - _Text is automatically available
define view Z_CONSUMER as select from Z_BASE
{
  key matnr,
      _Text  -- Propagated from Z_BASE
}

Blocking Propagation

@Metadata.ignorePropagatedAnnotations: true
define view Z_NO_PROPAGATION as select from Z_BASE
{
  key matnr
  // _Text NOT available unless explicitly defined
}

Composition Associations

For parent-child relationships in RAP:

define view entity Z_SALES_ORDER
  as select from vbak
  composition [0..*] of Z_SALES_ORDER_ITEM as _Items
{
  key vbeln,
      erdat,
      _Items
}

define view entity Z_SALES_ORDER_ITEM
  as select from vbap
  association to parent Z_SALES_ORDER as _Header
    on $projection.vbeln = _Header.vbeln
{
  key vbeln,
  key posnr,
      matnr,
      _Header
}

Accessing Associations in ABAP

Using Path Expression

SELECT
  vbeln,
  \_Customer-name1 AS customer_name,
  \_Customer-ort01 AS customer_city
FROM z_sales_order
INTO TABLE @DATA(lt_result).

Using Exposed Association

SELECT FROM z_sales_order
  FIELDS vbeln,
         \_Customer[ ]-name1 AS customer_name
INTO TABLE @DATA(lt_result).

Performance Optimization

TO ONE Optimization

SAP HANA optimizes TO ONE cardinality:

• Join can be pruned if target fields not selected
• Better query plan generation

-- Good: Enables optimization
association [0..1] to kna1 as _Customer on ...

-- Avoid if actually single record:
association [0..*] to kna1 as _Customer on ...

Cardinality Warnings

Set correct cardinality to avoid:

1. Syntax warnings in ADT
2. Unexpected duplicate rows
3. Performance issues

Common Patterns

Master Data Text Association

association [0..1] to makt as _Text
  on $projection.matnr = _Text.matnr
 and _Text.spras = $session.system_language

{
  key matnr,
      _Text.maktx as MaterialDescription
}

Currency/Unit Association

association [0..1] to tcurc as _Currency
  on $projection.waers = _Currency.waers

{
  waers,
  @Semantics.amount.currencyCode: 'waers'
  netwr,
  _Currency
}

Hierarchical Data

association [0..1] to Z_CATEGORY as _Parent
  on $projection.parent_id = _Parent.category_id
association [0..*] to Z_CATEGORY as _Children
  on $projection.category_id = _Children.parent_id

Restrictions

1. No to-many in WHERE for extend view: Cannot filter on [n..*] associations in view extensions
2. Cardinality must match data: Mismatched cardinality causes warnings/errors
3. No aggregate on associations: Cannot use SUM/AVG directly on associated fields
4. Path depth limits: Very deep paths may impact performance

Documentation Links

• SAP Help - Associations: https://help.sap.com/doc/abapdocu_752_index_htm/7.52/en-us/abencds_f1_association.htm
• SAP Community - Cardinality: https://community.sap.com/t5/enterprise-resource-planning-blog-posts-by-sap/cardinality-of-association-in-cds-view/ba-p/13351899
• New Cardinality Syntax: https://community.sap.com/t5/application-development-and-automation-blog-posts/new-cardinality-syntax-for-performance-optimization-in-abap-cds-and-abap/ba-p/13554546

Last Updated: 2025-11-23