Hello,

I just accidentally called Session.save() on an object that was loaded by that same session. And it worked perfectly - it updated the object with the values I had set.

Until now I had the impression that you should call save() on new objects that should be inserted and update on an existing object. So have I misunderstood the purpose of save() or this is just a lucky case where this worked but I shouldn't rely on it?

save(), update(), saveOrUpdate() on an object attached in the session is silently ignored.

Hibernate is not sending the update because of your sess.save() call.
It likely detected the change to the loaded object.

Generally you want to use sess.save when you are doing an insert.

When doing an update, generally the model is
session.load (object)
//call setters on object
tx.commit

no explicit sess.save needed- hibernate proxies your objects, so it "knows" the object is dirty.