Message type: E = Error
Message class:  SDDIC_DDLA_ANNOCHECK - Messages for annotation usage check 
Message number: 309
Message text: Unchecked expressions are not allowed for annotation reference values
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The SAP error message SDDIC_DDLA_ANNOCHECK309 indicates that there are unchecked expressions being used in annotation reference values within your ABAP code or data model. This error typically arises when you are working with annotations in the context of Core Data Services (CDS) views or other ABAP development scenarios where annotations are used to enhance the metadata of your data models.
Cause: The error occurs when: Annotations are defined in a way that references expressions that are not properly checked or validated. The expressions used in the annotation reference values are not deterministic or do not conform to the expected types or structures. There may be a syntax error or logical error in the way the annotations are defined.
Solution: To resolve this error, you can take the following steps: Review the Annotations: Check the annotations in your CDS view or ABAP code. Ensure that all expressions used in the annotation reference values are valid and properly defined. Check Expression
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