import warnings
import sqlalchemy
import sqlalchemy.orm

Base = sqlalchemy.orm.declarative_base()


class Resource(Base):
    __tablename__ = 'resource'

    id = sqlalchemy.Column(
        sqlalchemy.Integer, primary_key=True
    )
    _type = sqlalchemy.Column(
        sqlalchemy.String(50)
    )

    do_not_load = sqlalchemy.Column(
        sqlalchemy.Integer
    )
    __mapper_args__ = {
        'polymorphic_on': '_type',
        'polymorphic_identity': 'resource'
    }


class User(Resource):
    __tablename__ = 'user'

    id = sqlalchemy.Column(
        sqlalchemy.Integer, sqlalchemy.ForeignKey(Resource.id), primary_key=True
    )

    __mapper_args__ = {
        'polymorphic_identity': 'user'
    }


class Manager(Base):
    __tablename__ = 'manager'

    id = sqlalchemy.Column(
        sqlalchemy.Integer, primary_key=True
    )

    parent_id = sqlalchemy.Column(
        sqlalchemy.Integer, sqlalchemy.ForeignKey(User.id)
    )

    user = sqlalchemy.orm.relationship(
        User
    )


engine = sqlalchemy.create_engine(
    'sqlite:///:memory:', echo=True
)


Base.metadata.create_all(engine)

Session = sqlalchemy.orm.sessionmaker(
    bind=engine
)

session = Session()

user_alias = sqlalchemy.orm.aliased(User, flat=True)
manager_alias = sqlalchemy.orm.aliased(Manager, flat=True)


q1 = session.query(
    Manager
).join(
    User, Manager.user.of_type(user_alias)
).options(
    sqlalchemy.orm.contains_eager(
        Manager.user.of_type(User)
    ).load_only(
        User.id,
    )
)


q2 = session.query(
    manager_alias
).outerjoin(
    user_alias, manager_alias.user.of_type(user_alias)
).options(
    sqlalchemy.orm.contains_eager(
        manager_alias.user.of_type(user_alias)
    ).load_only(
        user_alias.id,
    )
)


q3 = session.query(
    manager_alias
).options(
    sqlalchemy.orm.joinedload(
        manager_alias.user.of_type(user_alias)
    ).load_only(
        user_alias.id,
    )
)

for label, query in (
    ('without_aliases', q1),
    ('with_aliases_contains_eager', q2),
    ('with_aliases_joinedload', q3)
):
    if str(query).count('do_not_load'):
        print('Warning: {0} contains do_not_load: {1}'.format(label, query))