On Feb 7, 2008, at 1:33 PM, Richard Levasseur wrote:
> For the syntax of it, I'd go for something like > `child_obj.change_from(parent_obj)` or `child_obj = > ChildClass.create_from(parent_obj)`, perhaps implicitly invoked when > you do child_obj.type = parent_obj. Not sure about that last part, > doesn't seem pythonic, and feels misleading. The point is to allow > the child the ability to perform custom operations if need be > (__change_type__?). Is the `session` part really necessary (I thought > objects knew what session, if any, they were attached to?). I don't > recall exactly if this is possible, but perhaps the child can have its > __dict__ set to the parent's? That'd preserve any state and wouldn't > require any loop-copy of attributes. the "session" part is introduced only in that we try not to attach lots of methods and accessors to user-defined classes. we like to leave user-defined classes as unmodified as possible which at the very least helps with the possibility of name collisions (like, if someones SA app has a "change_from" method already, this change would break their app). since everything else comes from "session" (like expunge(), refresh(), etc) this is where we like to put these things for consistency. however, thinking further about this I think how we'd actually do this would be the same way we do a "primary key switch" - the mapper already knows how to detect the "delete" of one instance and the "insert" of another, both with the same primary key attributes, and turn it into an "update". So i would see this as an extension to that functionality, i.e.: parent = sess.query(Parent).get(1) child = Child(id=1) child.someattr = parent.someattr # copy attributes sess.delete(parent) sess.save(child) sess.flush() --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
