if self.data is a BTree and I do: obj = self.data[id] obj.revsub = obj.revsub + 1 obj's class subclasses Persistant, as does self's Do I need to let the persistence mechanism know something has changed? If so, do I do: obj._p_changed=1 ...or... self._p_changed=1 (which feels like it's gonna store much more data than it needs to...) ...or something else? cheers, Chris