> I expect that foo.user_id does not exist, because that representation has been transformed into an object. Or you can just consider user_id to be a reference

> I expect that foo.user_id does not exist, because that representation has been transformed into an object. Or you can just consider user_id to be a reference pointer that is part of foo, while user.id is an attribute of user. Totally different things and I am glad that the distinction is there.