Marcin Krol wrote: > > Hello everyone, > > I have tested that session.add(changed_sqla_object) in at least one > context (when the object with id of changed_sqla_object already exists > in the db) does issue UPDATE sql query and updates the object in the > database. > > However, there's also session.update() method. Help on this says: > >> update(self, instance) method of sqlalchemy.orm.session.Session instance >> Bring a detached (saved) instance into this ``Session``. > > Meaning this updates session with the saved object data, and it's not > that the *changed* object's data that is updated in database? > >> >> Use session.add() > > To do what? > >> >> If there is a persistent instance with the same instance key, but >> different identity already associated with this ``Session``, an >> InvalidRequestError exception is thrown. >> >> This operation cascades the `save_or_update` method to associated >> instances if the relation is mapped with ``cascade="save-update"``. > > In general, the question: is it safe to use session.add(changed_object) > in *all of the circumstances*?
update(), save_or_update(), save() are all deprecated. add() places an object in the session in all cases, using the persistence information already associated with the object to determine INSERT or UPDATE. this means if you just make a new Foo(id=some id), that's transient - SQLAlchemy didn't load it. It will be INSERTed. Keep in mind that the Session maintains an identity map of all unique primary keys already loaded into memory, as well as the state which was received from the database. For this reason, you generally can't just put an object in the session with some arbitrary data, and expect it to "take the place" of the actual row that would be loaded by the transaction. SQLAlchemy wouldn't know what to do with it since it has no idea what changes have been made to this row versus what is already present. If you'd like to create a new Foo() with a primary key that may or may not already exist in the database, you want to merge the state of that object with one that is produced by the Session. Use session.merge() for this use case. this will load the existing object from the current transaction, if any, and merge the state of your outside object with it, returning the instance. The instance you pass to it remains unchanged and outside the session. --~--~---------~--~----~------------~-------~--~----~ 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 sqlalchemy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
