Eclipselink performs an unexpected insert in a many-to-one relationship - jpa

Question

I have a very basic relationship between two objects:
#Entity
public class A {
#ManyToOne(optional = false)
#JoinColumn(name="B_ID", insertable=false, updatable=true)
private StatusOfA sa;
getter+setter
}
#Entity
public class StatusOfA {
#Id
private long id;
#Column
private String status;
getter+setter
}
There's only a limited set of StatusOfA in DB.
I perform an update on A in a transaction:
#TransactionalAttribute
public void updateStatusOfA(long id) {
A a = aDao.getAById(123);
if(a != null) {
a.getStatusOfA().getId(); //just to ensure that the object is loaded from DB
StatusOfA anotherStatusOfA = statusOfADao.getStatusOfAById(456);
a.setStatusOfA(aontherStatusOfA);
aDao.saveOrPersistA(a);
}
}
The saveOrPersistA method is here merging 'a'.
I expect Eclipselink to perform only an update on 'a' to update the StatusOfA but it's executing a new insert on StatusOfA table. Oracle is then complaining due to a unique contraint violation (the StatusOfA that Eclipselink tries to persist already exists...).
There is no Cascading here so the problem is not there and Hibernate (in JPA2) is behaving as excepted.
In the same project, I already made some more complex relationships and I'm really surprised to see that the relation here in not working.
Thanks in advance for your help.

Answer 1

What does, statusOfADao.getStatusOfAById() do?
Does it use the same persistence context (same transaction and EntityManager)?
You need to use the same EntityManager, as you should not mix objects from different persistence contexts.
What does saveOrPersistA do exactly? The merge() call should resolve everything correctly, but if you have really messed up objects, it may be difficult to merge everything as you expect.
Are you merging just A, or its status as well? Try also setting the status to the merged result of the status.

Answer 2

Assumptions: #Id#GeneratedValue(strategy = GenerationType.IDENTITY)
Let's consider the following implementations of statusOfADao.getStatusOfAById(456) :
1. returns "proxy" object with just id set:
return new StatusOfA(456);
2. returns entity in new transaction:
EntityManager em = emf.createEntityManager();em.getTransaction().begin();
StatusOfA o = em.find(StatusOfA.class,456);//em.getReference(StatusOfA.class,456);
em.getTransaction().commit();
return o;
3. returns detached entity:
StatusOfA o = em.find(StatusOfA.class,456);//em.getReference(StatusOfA.class,456);
em.detached(o);
return o;
4. returns deserialized-serialized entity:
return ObjectCloner.deepCopy(em.find(StatusOfA.class,456));
5. returns attached entity:
return em.find(StatusOfA.class,456);
Conclusions:
Eclipselink handles only implementation N5 as "expected".
Hibernate handles all five implementations as "expected".
No analisys of what behaviour is jpa spec compliant