I have some code that results in the exception: Illegal attempt to associate a collection with two open sessions

Searching via Google this seems to occur in a number of situations, but none of the other situations seems to fit what I am seeing. For example, I do not use @ManyToOne(cascade = CascadeType.ALL) anywhere.

I always use .getCurrentSession() to get a session, so I am not clear on how I could have two open sessions.

Does anyone have any other suggestions on why this might happen?

So, the fix seems to be to use session.merge() instead of session.update() - but I still do not know why hibernate thinks I have more than one session open. I cannot seem to find anything in the API to detect if another session is already open.

Given there are so many different causes of this exception, it would be nice if the hibernate diagnostics were a little more specific as to what the cause might be.