Question

如何实现自我引用的多对多关系，这种关系实际上是两个其他关系的结合？

该关系应返回用户与网络中其他用户之间存在的所有FacebookFriendship模型。用户可能拥有指向另一个现有用户的FacebookFriendship，但由于FB API中断，隐私控制等，现有用户可能不存在镜像FBFriendship给该用户。

# This class is necessary for python-social-auth
# A UserSocialAuth model only exists for users who are in the network
class UserSocialAuth(_AppSession, Base, SQLAlchemyUserMixin):
    """Social Auth association model"""
    __tablename__ = 'social_auth_usersocialauth'
    __table_args__ = (UniqueConstraint('provider', 'uid'),)
    id = Column(Integer, primary_key=True)
    provider = Column(String(32))
    uid = Column(String(UID_LENGTH))
    extra_data = Column(JSONType())
    user_id = Column(
        Integer, ForeignKey(User.id), nullable=False, index=True)
    user = relationship(
        User,
        backref=backref('social_auth', lazy='dynamic')
    )

此关系发现FacebookFriendship模型指向此用户指向任何现有用户。

    facebook_friendships = relationship(
        FacebookFriendship,
        primaryjoin=and_(
            user_id == FacebookFriendship.user_id,
            provider == 'facebook'
        ),
        secondary=FacebookFriendship.__table__,
        secondaryjoin=uid == FacebookFriendship.fb_uid_friend,
        foreign_keys=[provider, user_id, uid],
        viewonly=True,
        uselist=True,
        lazy='dynamic',
    )

此关系找到指向此用户的FacebookFriendship模型。

    other_facebook_friendships = relationship(
        FacebookFriendship,
        primaryjoin=and_(
            uid == FacebookFriendship.fb_uid_friend,
            provider == 'facebook'
        ),
        foreign_keys=[provider, uid],
        viewonly=True,
        uselist=True,
        lazy='dynamic',
    )

我能够使用hybrid_property装饰器来表达联合查询，但是这可以防止像any（）或使用关联代理这样的比较器的使用，至少从我能说的就是这样。

    # Can I rewrite this using relationship()?
    @hybrid_property
    def all_facebook_friendships(self):
        return self.facebook_friendships.union(
            self.other_facebook_friendships).correlate(
            FacebookFriendship)

# FBFriendship models are created for every friend that a user has,
# regardless of whether they're in the network or not.
class FacebookFriendship(Base):
    __tablename__ = u'user_fb_friend'

    user_id = Column(Integer, sa.ForeignKey(User.id), primary_key=True)

    user = relationship(
        User, backref=backref('facebook_friendships', lazy='dynamic'),
        primaryjoin=User.id == user_id)

    fb_uid_friend = Column(sa.String(length=255), primary_key=True)

最后，我想像任何其他InstrumentedAttribute一样查询这种关系： UserSocialAuth.query.filter(UserSocialAuth.all_facebook_friendships.any()).all() 并在User模型上定义association_proxy：

User.all_facebook_friends = association_proxy('all_facebook_friendships', 'user')

对不起这个问题的篇幅，但我已经试过了。现在几天都没有用了。

SQLAlchemy：如何将关系定义为另外两个关系的并集？

1 个答案: