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Re: [eclipselink-users] EntityManager.remove does not remove entity from cache
There may be an enhancement request in there somewhere. Please feel free to enter one.
At the moment the JPA specification requires that you maintain your relationships and does not mandate any automatic relationship maintenance by the provider. 

-Tom

Mike Traum wrote:

Sure. Here's a snippet:

   EntityManager em = emf.createEntityManager();
   Query q = em.createQuery("select a FROM A a");
   List<A> as = q.getResultList();
   em.clear();
   em.close();
     B b = as.get(0).getChildren().get(0);
   System.out.println(b.getId()); // prints '2'
     em = emf.createEntityManager();
   em.getTransaction().begin();
   B bm = em.merge(b);
   em.remove(bm);
em.getTransaction().commit(); // successfully removes b with id '2' from database 
   em.clear();
   em.close();
     em = emf.createEntityManager();
   q = em.createQuery("select a FROM A a");
   as = q.getResultList();
   b = as.get(0).getChildren().get(0);
   System.out.println(b.getId()); // prints '2'
   boolean contains = em.contains(b);
   System.out.println(contains); // prints 'true'
   em.clear();
   em.close();


mike

Tom Ware wrote:

I am not sure I follow.   Can you provide a code sample?

Mike Traum wrote:

Tom,
I see where you're coming from. The spec references that you gave do seem to support this behavior (unfortunate, but that's an issue for a different list). But, I think you then run into other conflicts with the spec. For example, contains on that the removed entity will return true after retrieving it with the query. 

Section 3.2.5
The contains method returns true:
• If the entity has been retrieved from the database, and has not been removed or detached. • If the entity instance is new, and the persist method has been called on the entity or the persist 
operation has been cascaded to it.

The contains method returns false:
• If the instance is detached.
• If the remove method has been called on the entity, or the remove operation has been cascaded 
to it.
• If the instance is new, and the persist method


mike


mike

Tom Ware wrote:
The spec references I have found are in section 3.2.3 of the JPA 1.0 specification: 

Reference 1:
---
Bidirectional relationships between managed entities will be persisted based on references held by the owning side of the relationship. It is the developer’s responsibility to keep the in-memory references held on the owning side and those held on the inverse side consistent with each other when they change. 
---

Reference 2: (for flushing)

----
The semantics of the flush operation, applied to an entity X are as follows: 

<snip>
- If X is a removed entity, it is removed from the database. No cascade options are relevant. 
----

Is there something I am missing in the spec that you can point me to?

-Tom


Mike Traum wrote:
Maybe I've been defining my entities strangely, but if you define a @OneToMany on A and then a @ManyToOne on B (pointing to A), the schema generated by eclipselink will have the foreign key in B pointing to A. So, this will not be enforced by the database. I can drop in some code to illustrate if desired.
If the above is not funky, I think, by the JPA spec, the DB delete should not occur. Otherwise, the relationship 'magic' will occur between app restarts but not within app queries. 

mike

Tom Ware wrote:
EclipseLink relies on your DB foreign-key-contstraints to enforce this.
i.e. You should get a SQL exception on the remove if a foreign-key-constraint exists for this relationship. 

Mike Traum wrote:
Yes, I thought that might be the answer. But, the implementation seems odd. JPA doesn't provide magic for this, but it is deleted from the database, however the cache is maintained in a stale state. It seems to me that either it should not be deleted from the database or it should be removed from the cache. 

mike

Tom Ware wrote:

Hi Mike,
You need to sever the relationship between an A and a B before you remove B. JPA does not provide any magic for this. 

-Tom

Mike Traum wrote:

I have the following enitiy map:
A->B->C (where -> represents a OneToMany relationship)
If I do a EntityManager.remove on a B, a following Query (select all) will still return that entity, even though it has been removed from the database. 

Any ideas on the proper way to handle this?

Here's some code illustrating the issue:
   EntityManager em = emf.createEntityManager();
   Query q = em.createQuery("select a FROM A a");
   List<A> as = q.getResultList();
   em.clear();
   em.close();
System.out.println(as.get(0).getChildren().size()); // output is 2 
     B b = as.get(0).getChildren().get(0);
     em = emf.createEntityManager();
   em.getTransaction().begin();
   B bm = em.merge(b);
   em.remove(bm);
em.getTransaction().commit(); // successfully removes B and children from database 
   em.clear();
   em.close();

   em = emf.createEntityManager();
   q = em.createQuery("select a FROM A a");
   as = q.getResultList();
   em.clear();
   em.close();
System.out.println(as.get(0).getChildren().size()); // output is 2 
     em = emf.createEntityManager();
   q = em.createQuery("select a FROM A a");
((ReadAllQuery)((EJBQueryImpl)q).getDatabaseQuery()).refreshIdentityMapResult(); 
   as = q.getResultList();
   em.clear();
   em.close();
System.out.println(as.get(0).getChildren().size()); // output is 1 


Thanks,
Mike

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