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Design Specification: TREAT expression support

ER 374771

Document History

Date Author Version Description & Notes
20 March 2012 Gordon Yorke Initial Document created

Project overview

JPA 2.1 will add support for a TREAT function within JPQL and criteria. Support will be required for both JPQL and Criteria queries.


When creating a JOIN in a JPQL statement or Criteria API expression the type of the join is that of the corresponding attribute type. Should the query writer wish to reference an attribute of a subclass of that JOIN type the query writer would use the TREAT function to effectively join to a subclass of the JOIN type and JOIN is treated as the specified subtype.

 Select e from Employee e, JOIN TREAT(e.projects as LargeProject) l WHERE l.budget > 25000 

In the case of this example the type of Employee.projects is Project. Because the query writer wants to access an attribute of the subclass LargeProject TREAT is used.


Support use of the TREAT keyword in JPQL and Criteria API for FROM and WHERE clauses. Ensure proper validation exceptions occur.

Design Constraints

Design / Functionality




Config files


Work Required

  1. Implement expression framework support for WHERE clause
    approx 3 days
  2. Implement JPQL support
    approx 2 day
  3. Implement Criteria support
    approx 2 days
  4. Testing
    approx 2 days

Open Issues

This section lists the open issues that are still pending that must be decided prior to fully implementing this project's requirements.

Issue # Owner Description / Notes


This section lists decisions made. These are intended to document the resolution of open issues or constraints added to the project that are important.

Issue # Description / Notes Decision

Future Considerations

During the research for this project the following items were identified as out of scope but are captured here as potential future enhancements. If agreed upon during the review process these should be logged in the bug system.

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