Transaction and scopedsession (SQLAlchemy & Pyramid)

myapp.model.__init__.py

from sqlalchemy.orm import sessionmaker, scoped_session

...

Session = scoped_session(sessionmaker())

# When using scoped_session, Session and Session() expose the same .commit() .query() .add() etc. methods.

...

myapp.model.user.py

from myapp.model import Session, Base


class User(Base):

    ...

    # User model is using the myapp.model's Session to perform pre-insert and pre-update

    # And there are some other methods like:

    @classmethod
    def get_by_name(cls, name):
        return Session.query(...)

    # And some other that might write stuff:

    def set_name(self, name):
        self.name = name
        Session.add(self)
        Session.commit()
        # Printing the Session here gives
        # <sqlalchemy.orm.scoping.ScopedSession object at 0x1038b95d0>

        # When running the tests, will give me:
        # InvalidRequestError: Object '<User at 0x104ee5350>' is already attached to session '1' (this is '2')

    pass

myapp.tests.__init__.py

# From http://sontek.net/blog/detail/writing-tests-for-pyramid-and-sqlalchemy

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker


class MyAppTest(unittest.TestCase):

    @classmethod
    def setup_class(cls):
        cls.engine = create_engine(
            'mysql://...@127.0.0.1:3306/myapptest?charset=utf8&use_unicode=0',
            echo = False,
        )

        cls.Session = sessionmaker()

    def setUp(self):
        connection = self.engine.connect()

        # begin a non-ORM transaction
        self.trans = connection.begin()

        # bind an individual Session to the connection
        self.session = self.Session(bind=connection)

        # HERE'S THE QUESTION
        # Since the model also writes stuff to the db (see dummy function User.set_name below), I also need
        # to make sure Session is wrapped in a Session, do I?

        # Here is my naive tentative
        from myapp import model

        # This line gives "InvalidRequestError: Scoped session is already present; no new arguments may be specified."
        # when the second test is run
        model.Session(bind=connection)

        print "in test.setUp: self.session: %s" % self.session
        # Prints <sqlalchemy.orm.session.Session object at 0x106fdee90>
        print "in test.setUp: model.Session: %s" % model.Session
        # Prints <sqlalchemy.orm.scoping.ScopedSession object at 0x105f195d0>

        from myapp.model import Session
        print "in test.setUp: Session: %s" % Session
        # Prints <sqlalchemy.orm.scoping.ScopedSession object at 0x105f195d0>

myapp.tests.test_whatever.py

from myapp.tests import MyAppTest
from myapp.model.user import User

class TestWhatever(MyAppTest):

    user = User(name="Charles")

    def setUp(self):
        # Installing some fixtures
        self.session.add(self.user)
        self.session.flush()

    def test_set_name(self):
        # Just as an example, obviously not an actual test
        self.user.set_name("Maxwell")
        self.assertEqual(self.user.name, "Maxwell")

    def test_set_name2(self):
        # Just as an example, obviously not an actual test
        self.user.set_name("John")
        self.assertEqual(self.user.name, "John")