Reattaching a detached instance: hibernate lock()

it fixes the issue Can you use a fresh session (or transaction) for processing each item and for updating the UserSetting? This would probably prevent the NonUniqueException.
Cheers,

around this issue I think you can just use the detached Object o and after just to use the session.update(o).
Try to watch this video tutorial, maybe it will be useful!

this will help What I did is, instead of a map, use separate collections for the parent and child objects. After that I just persisted the parent object collection and that was It (because child object can't exist without a parent object, but parent can without child objects, otherwise I could also instead persist the child objects).
So the problem with map was, that although you add a value to a specific keys collection values from another keys collection values, It does not reference the same object, i.e. It creates a new one for the other key collection, which is why in this case you get duplicates when persisting the key values (which are the parent objects).

hope this fix your issue Ok, figured out, It was missing the @Stateless annotation in my test class... that did the trick, thanks anyway

This might help you
The architecture I'm using in my program is that the data access layer is abstracted from the application.