def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def test_config_errors(self):
        Session = scoped_session(sa.orm.sessionmaker())

        s = Session()  # noqa
        assert_raises_message(
            sa.exc.InvalidRequestError,
            "Scoped session is already present",
            Session,
            bind=testing.db,
        )

        assert_warns_message(
            sa.exc.SAWarning,
            "At least one scoped session is already present. ",
            Session.configure,
            bind=testing.db,
        )