How To Fix SDDL_PARSER_MSG238 - Compositions are not allowed in CDS views with Union and Union All

SAP Error Message - Details

• Message type: E = Error

• Message class: SDDL_PARSER_MSG - Message Class for DDL Parser

• Message number: 238

• Message text: Compositions are not allowed in CDS views with Union and Union All

Self-Explanatory Message

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Smart SAP Assistant

• What is the cause and solution for SAP error message SDDL_PARSER_MSG238 - Compositions are not allowed in CDS views with Union and Union All ?

  The SAP error message SDDL_PARSER_MSG238 indicates that there is an issue with the use of compositions in Core Data Services (CDS) views that utilize UNION or UNION ALL operations. This error arises because compositions (which are essentially associations or relationships between entities) are not permitted in CDS views that combine multiple result sets using these operations.
  Cause
  The primary cause of this error is the attempt to define a CDS view that includes compositions while also using UNION or UNION ALL. In CDS views, compositions are used to define relationships between entities, but when you perform a union operation, the resulting structure must be flat and cannot maintain the hierarchical relationships that compositions represent.
  Solution
  To resolve this error, you have a few options:
  
  
  Remove Compositions: If possible, refactor your CDS view to eliminate any compositions. Instead, you can use simple fields or associations that do not require a hierarchical structure.
  
  
  Separate Views: Create separate CDS views for each part of the union that do not include compositions. You can then use these views in your union operation.
  
  
  Use Associations: If you need to maintain some form of relationship, consider using associations instead of compositions. However, be aware that associations also have limitations when used with unions.
  
  
  Flatten the Structure: If your use case allows, flatten the data structure so that you can represent the necessary information without using compositions.
  
  
  Related Information
  
  CDS Views: Core Data Services (CDS) is a framework for defining semantically rich data models in SAP. Understanding how to structure your CDS views is crucial for avoiding such errors.
  UNION and UNION ALL: These SQL operations combine the results of two or more SELECT statements. The resulting dataset must have the same number of columns and compatible data types.
  SAP Documentation: Refer to the official SAP documentation for CDS views and the specific limitations regarding unions and compositions. This can provide additional context and examples.
  
  Example
  If you have a CDS view defined as follows:
  define view ZMyView as
  select from TableA
  union all
  select from TableB
  And you try to include a composition like this:
  define view ZMyView as
  select from TableA
    association [0..1] to TableC as _TableC on $projection.FieldA = _TableC.FieldA
  union all
  select from TableB
  You will encounter the error. Instead, you should separate the views or remove the association.
  By following these guidelines, you should be able to resolve the error and successfully create your CDS views without encountering the SDDL_PARSER_MSG238 message.