def test_custom_join(self):

        users, items, order_items, orders, Item, User, Order = (
            self.tables.users,
            self.tables.items,
            self.tables.order_items,
            self.tables.orders,
            self.classes.Item,
            self.classes.User,
            self.classes.Order)

        mapper(Item, items)

        mapper(Order, orders, properties=dict(
            items=relationship(Item, order_items)))

        mapper(User, users, properties=dict(
            orders=relationship(Order)))

        session = create_session()
        l = (session.query(User).
             select_from(users.join(orders).
                         join(order_items).
                         join(items)).
             filter(items.c.description == 'item 4')).all()

        eq_(l, [self.static.user_result[0]])
select_from totally replace the FROM parameters.
dataset/ETHPy150Open zzzeek/sqlalchemy/test/orm/test_mapper.py/MapperTest.test_custom_join