Pyramid / SQL Alchemy DetachedInstanceError

Question

I'm trying to implement email confirmation using Pyramid framework. Here's the code that confirms the user in the database and redirects them to the home page.

   user = DbSession.query(User).filter_by(email=email).one()     
   if user.approved:
       return {'msg': _('Already approved')}        
   if user.check_approve_token(hash):
       user.approved = True
       self.request.session.save()
       self.request.session['user'] = user
       return HTTPFound(self.request.route_url('home'),
                            headers=remember(self.request, user.guid))

When I try to get the self.request.session['user'] variable from another handler, I get a DetachedInstanceError: Instance <User at 0x42902f0> is not bound to a Session; attribute refresh operation cannot proceed. As far as I understand, this error raised because of the modification of User instance. How can I fix it?

Thanks in advance, Ivan.

Answer 1

The error is because model objects (user) are managed by the session (DbSession). When you store the instance in a session (request.session) and then access it again in another request, this is using a different DbSession. Moving a managed object between sessions is supported, but not automatically. When retrieving the object from the request.session, you can merge it into your new DbSession via user = DbSession.merge(user).

http://docs.sqlalchemy.org/en/latest/orm/session.html?highlight=merge#merging