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jpaeclipselink

Purpose of Eclipselink 2.6.0 query - SELECT ID FROM TBL WHERE ID=?

Has anyone got an idea why JPA Provider - Eclipselink (using version 2.6.0) generates query like:

SELECT ID FROM OPERATION WHERE (ID = ?);

or

SELECT ID FROM SUBSCRIPTION WHERE (ID = ?);

Why it needs to get ID providing an ID...

Maybe 1st or 2nd level Cache synchronization? Maybe my queries are inaccurate... In my queries I never ask directly this to execute - I use JPQL and never ask for ID giving some ID.

I have quite complex model and queries so I see no point in providing full code (or only if U really insist but I dont think it will help a lot). Using Oracle 12c DB.

Solution

  • We have encountered the same issue with our Java application using EclipseLink 2.5.2. Specifically, we saw it whenever we inserted a new entity that had a M:1 relationship with another entity. A simplified use case would be:

    A a = new A(); // the new entity
B b = lookupB(); // get existing entity from database
a.setB(b); // set M:1 relationship
em.persist(a); // save

    In this case, we would always see a query for B (i.e., SELECT ID FROM B WHERE ID = @). After some research, we traced it down to the existence checking that EclipseLink performs before merging records.

    We found that annotating the entity class for B with @ExistenceChecking(ExistenceType.ASSUME_EXISTENCE) prevented EclipseLink from running the query.

    For a further discussion of this, see this related post.