Hi,

So I'm using the common ThreadLocal pattern in Tomcat. Each request gets its own Session, which is closed when the request terminates.

My application stores a persistent instance that was loaded with Session.load() on the Tomcat session. At the beginning of each request the instance is re-associated with the current request's session using:



This was working perfectly well until I introduced a JCS JVM-level cache. Now I get the error:



So, how do I check for this condition? And if it's already associated with the session, how do I get the instance that is associated with the session? I was previously checking



but this doesn't prevent the exception anymore.

Thanks,

In case anyone is interested this was the problem:

Of course Hibernate requires that there be only one java instance of a persistent entity per Hibernate session. Session.load(instance) will not always work well with this requirement because it is trying to bind another java instance to the persistent entity.

Before I added the cache, the order of events was:
1. re-associated the instance saved on the HTTP session with the persistent entity using Session.load(instance).
2. accessed the same entity as one member of a one-to-many lazy persistent collection

Since the Hibernate session controls the contents of a lazy persistent collection, this order was not creating another java instance of the same entity, it was only just returning the instance that had originally been on the HTTP session.

After I added the cache, the entity owning the lazy collection was saved on the cache and the object graph containing this entity happened to be accessed before I was re-associating the instance from the HTTP session with the current Hibernate session. Thus the order was:
1. accessed the same entity as one member of a one-to-many lazy persistent collection (from object graph stored in cache)
2. re-associated the instance saved on the HTTP session with the persistent entity using Session.load(instance)

This ordering is problematic because step 2 tries to associate another java instance with the persistent entity, which is illegal if there is a pre-existing java instance already so associated.

So, the solution I came up with is to re-associate the instance from the HTTP session this way:



which solved the previous problem.

Just wondering, why are you using .load() instead of .update()? I thought update was the preferred method of reassociating an object with a session???

You can use update or in 2.1 use the lock to associate without accessing the db.