Question

I need to attach an object to session in such a way that it will not differ from one persisted in db. (Easier to explain it with code):

session.query(type(some_object)).filter_by(id=some_object.id).one()

Is there more proper way to do that?
session.add(some_object) doesn’t work since an entity with such id can already be attached to this session, and object = session.merge(some_object) doesn’t work for me because it translates state from detached copy (if i make object.name=’asdfasdf’ these changes will be pending after merging object)

EDIT:

I found a bit less ugly way:

some_object = session.merge(some_object)
session.refresh(some_object)

But is there a way todo this in one call?

Answer 1

I need to attach an object to session in such a way that it will not differ from one persisted in db.

“will not differ from DB” pretty much means you’re looking to load it, so query it. You might want to consider that the object might already be present in that target session. so your approach with query(type(object)) is probably the most direct, though you can use get() to hit the primary key directly, and populate_existing() to guarantee that state which already exists in the session is overwritten:

session.query(type(some_object)).populate_existing().get(some_object.id)

the above calls down to almost the same codepaths that refresh() does. The merge/refresh approach you have works too but emits at least two SELECT calls.