Hibernate uses old closed SessionImpl instead of given SessionImpl - ajax

Question

I have a problem with Hibernate Enverse (Version 5.2.0-Final).
Context:
I'm auditing some entities with some lazy relations. I have a jsf-page that loads one version of one entity with all relations of that version. That works fine. So now I have a page that shows a revision of the entity with all relations of that revision. On this page I can open a fieldset, that triggers an AJAX. In this request we reattach all relations by calling entityManager.merge(entity) to be able to fetch the lazy relations in this fieldset. (The EntityManager is RequestScoped)
The Problem:
The AJAX is a new request. The server calls entityManager.merge(entity), what enforces creation of a new EntityManager (So a new org.hibernate.internal.SessionImpl is created). On this object hibernate calls SessionImpl.merge(...). But in the method org.hibernate.internal.AbstractSharedSessionContract.createQuery(String) a other SessionImpl object is used, which is already closed in the request before. That enforces an java.lang.IllegalStateException: Session/EntityManager is closed.
In one sentence: Although a new entityManager was created and a merge was called on that new entityManger, Hibernate uses an old Session/EntityManager of the request before.
I debugged the problem and found following:
Debug1: Shows the Stacktrace of the SessionImpl.merge(...) with the session's object id
Debug2: Shows the last method with the correct SessionImpl object (see it's id). This object is not used in next methods.
Debug3: The step after Debug2 does not know the given SessionImpl object. It has it's own SessionImpl object in collection.initializor.versionsReader. This session was created and closed in the request before (on loading the page).
Debug4: Now Hibernate wants to create the query wit the closed SessionImpl
Debug5: This enforces the exception, as the session is closed.
My questions:
Is this a bug of Hibernate?
Why is the given SessionImpl in method org.hibernate.type.CollectionType.getElementIterater(...) not used?
Anyone knows a solution or workaround for this problem?
Tank you very much for any idea. I spent days on this bug.

Answer 1

Why is the Session arg in o.h.type.CollectionType.getElementIterator not used?
The short answer is it isn't required, its simply a backward compatibility concern from 8 years ago.
The long answer is the type-system used to actually deviate some behavior based on whether or not the user had specified the session to operate in EntityMode.MAP or EntityMode.POJO and therefore the types needed to know what mode the session was in; hence why it was passed.
But even back in 2011 when this was changed, the session argument only ever influenced behavior if and only if the session was operating in EntityMode.MAP. In other words, all other modes always routed directly to the underlying collections Collection#iterator() method.
All this aside however, this doesn't have any impact on what you experience in your Debug3 screen-shot.
Is this a bug in Hibernate?
No, based on what I have read, I believe you're mixing concerns.
In Hibernate (no Envers), you can basically do this
// Request 1
request1EntityManager = getEntityManager();
sessionScopeEntity = request1EntityManager.find( MyEntity.class, myEntityId );
// Request 2
request2EntityManager = getEntityManager();
sessionScopeEntity = request2EntityManager.merge( sessionScopeEntity );
for ( SomeCollectionItem Item : sessionScopeEntity.getSomeCollection() ) {
// do things here
}
The above works because you reassociate the entity with the new session which in-turn injects the session into all the uninitialized proxies the entity maintains. But you can also rewrite the above as
// Request 1
request1EntityManager = getEntityManager();
sessionScopeEntity = request1EntityManager.find( MyEntity.class, myEntityId );
sessionScopeEntity.getSomeCollection().size() // initialize collection w/request1Session
// Request 2
request2EntityManager = getEntityManager();
for ( SomeCollectionItem Item : sessionScopeEntity.getSomeCollection() ) {
// do things here
}
The difference is the collection gets initialized with the first session and therefore when you attempt to access it with the second session, the entity doesn't necessarily need a merge because the collection is no longer a proxy but actually populated like a normal fetched collection would be.
The major difference between an entity instance returned by Hibernate and an audited entity instance returned by Envers is that the audited entity instance is NOT a managed persistent entity.
Depending on your scenario, you may decide to only audit a subset of fields on an entity mapping. This is why you cannot nor should not use things like merge with that instance as it could easily lead to unintended side effects with your real data.
If you intend to pass the audited entity instance across sessions, i would highly suggest that you instead consider initializing the collections you need up-front with the first session where you fetched the instance because presently there is no way to re-associate an audited entity instance with a new session.