After persist(A), A is in persisted but A.getB() is not

ge0ffrey · **Joined:** Thu Oct 13, 2005 4:19 am **Posts:** 98

I have A object which has a @ManyToOne to a B object.
From a different JVM I receive a transient A which references a detached B.
If I now persist A:

Code:

entityManager.persist(a);

then a is in the persistence context, but a.getB() is not.
This leads to problems. Does the spec allow to have a persistent object refer to a detached object?
Is there a specific reason why hibernate doesn't simply change the a.getB() with a proxy of B (or a persistent instance of B)?
Note that I don't want PERSIST/MERGE cascading from A to B.

If I now query that A (and it's B) from the database, like this:

Code:

A refreshedA = entityManager.createQuery("from A a left join fetch a.b left join fetch b.c where a.id = " + a.getId()).getSingleResult();

Then a.getB() is still the detached object (it's not in the persistent context) and even worse, the a.getB().getC() isn't loaded (even though I explicitly asked to fetch it in the query).

Thanks for any and all help.

sanne.grinovero · **Posted:** Wed Jun 02, 2010 5:58 am

that's natural you asked for that.
When you have A in the persistence context and then query for A, you will get the same reference back (A==A) because it was already in the persistence context. As you don't want it to cascade persist/merge B is still detached.

If you want these things to "just work" you should use cascade persist/merge. A hack for you could be to NOT attach A to the persistence context, just perform the query from a.getId().