I have defined a filter via @FilterDef and assigned it to an entity class through @Filter. I can't find a way to enable them via a persistence context though, without getting hold of the underlying Session -- and IIRC it is implementation-specific whether I can access it. (I'm using Glassfish which does, or at least used to, return a proxy to the EM implementation instead of a direct reference.) Can it be done?

Filter is much Hibernate specific stuff.
I looked under hints (http://www.hibernate.org/hib_docs/entit ... le/#d0e773), but it is not there.
So I think you cannot use it without referencing Session.

Re-reading what I wrote, I guess I wasn't too exact. I have nothing against accessing the Session and calling methods on it, What I can't do is calling something like ((EntityManagerImpl) em).getSession() to get a reference. I don't know any other way, though.

I've thought about adding a query hint that can be used to enable certain filters for the duration of that specific query, but I wanted to check first if there is some way I didn't notice. This solution isn't nice -- IMO, hints should only influence how a query is executed, and should not change the query substantially. But it's the least wrong way I could think of. (Unless the spec changes since the PFD include some means to access similar implementation-specific features. I don't know where to check this, though, or even whether I can check these changes.)

Try casting your EM to this interface - since it should be exposed.

public interface HibernateEntityManager extends EntityManager {
public Session getSession();
}

The next spec provides a em.getDelegate() method that will provide access to the Hibernate EM implementation( no wrapper )
They probablya re spec compliant in their CVS

Actually, it is there since build 38 or so, I just didn't spot this addition. Thanks.