Does Hibernate support upsert/merge? In other words, automatically insert the record if it doesn't exist in the database and automatically update the record if it already does exist?

I have come across a scenario where this would come in handy. I have numerous threads which can potentially write to the same record in a table. If the record doesn't exist, it is supposed to insert. If it does exist, it is supposed to update. The problem is some of threads step on each other, so I get a constraint violation when some of the threads tries to insert at the "same time."

I could catch the contraint violation and force an update, but I was wondering if there was any way to make Hibernate manage it. Thanks!

what is upsert?
anyhow there is session.saveOrUpdate().. but I think you are asking if there is a way to automate a merge of the object into the current session, if it is detached; and if that is the Q, then no I don't think there is - and you may get away with just calling session.saveOrUpdate(), having set the ID's properly on your objects (and in your mapping you'd need to specify the unsaved-value="null") - also assuming that your ID's are indeed objects and not literals.

What about session.merge( detachedInstance ) ?

Also, what constraint violation are you getting? Mapping documents would be helpful.