Poly*MixIn

gistfile1.py

class _Comparator(Comparator):
    def operate(self, op, other):
        discriminator, id = list(self.__clause_element__())
        return expr.and_(op(discriminator, other.__class__.__name__),
                         op(id, other.id))
    def in_(self, others):
        return expr.or_(*[self == o for o in others])
    def __clause_element__(self):
        cls = Comparator.__clause_element__(self)
        return expr.ClauseList(getattr(cls, "{0}_discriminator" \
                                           .format(self._prefix)),
                               getattr(cls, "{0}_id" \
                                           .format(self._prefix)))
class _CreatorComparator(_Comparator):
    _prefix = "creator"

class _ReceiverComparator(_Comparator):
    _prefix = "receiver"

class PolyCreatorMixIn(object):
    creator_discriminator = db.Column(db.String(50), nullable=False)
    creator_id = db.Column(db.Integer, index=True, nullable=False)
        
    @hybrid_property
    def creator(self):
        return getattr(self, "%s_creator" % self.creator_discriminator)

    @creator.setter
    def creator(self, creator):
        self.creator_discriminator = creator.__tablename__
        setattr(self, "%s_creator" % self.creator_discriminator, creator)
        
    @creator.comparator
    def comparator(cls):
        return _CreatorComparator(cls)

class PolyReceiverMixIn(object):
    receiver_discriminator = db.Column(db.String(50), nullable=False)
    receiver_id = db.Column(db.Integer, index=True, nullable=False)

    @hybrid_property
    def receiver(self):
        return getattr(self, "%s_receiver" % self.receiver_discriminator)

    @receiver.setter
    def receiver(self, receiver):
        self.receiver_discriminator = receiver.__tablename__
        setattr(self, "%s_receiver" % self.receiver_discriminator, receiver)

    @receiver.comparator
    def comparator(cls):
        return _ReceiverComparator(cls)