如何获取关联对象ie user.follows（）和user.followers（）的反向引用

Question

我正在尝试创建一个关联对象UserRelationship，它定义了User和User之间的“跟随”关系

class UserRelationship(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    follows_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    follower_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    follows = db.relationship("User", foreign_keys=[follows_id])
    follower = db.relationship("User", foreign_keys=[follower_id])
    bank = db.Column(db.Float)

    def __repr__(self):
        return f'{self.follower.username} follows {self.follows.username} with {self.bank}'



class User(UserMixin, db.Model):

    follows = db.relationship('UserRelationship',
                              primaryjoin=(UserRelationship.follower_id == id),
                              backref=db.backref('followers'),
                              lazy='dynamic')

    def follow(self, user, bank):
        if not self.is_following(user):
            new_follow = UserRelationship(bank=bank)
            new_follow.follows = user
            self.follows.append(new_follow)
            db.session.commit()
            return new_follow

    def unfollow(self, user):
        if self.is_following(user):
            relationship = self.follows.filter(UserRelationship.follows == user).first()
            db.session.delete(relationship)
            db.session.commit()
            return self.follows.all()

    def is_following(self, user):
        return self.follows.filter(
            UserRelationship.follows == user).count() > 0

这将在shell中产生预期的结果：

joe=User(username='joe')
paul=User(username='paul')
phil=User(username='phil')

phil.follow(joe,bank=123)
[phil follows joe with 123]

因此，当我user.follows时，我会被带到一个UserRelationship对象，我可以查询该对象以获得该用户跟踪的所有人。我明白了。我不明白的是如何让User.followers工作。我想要的是一个查询（或列表）或User.followers。backref命令无效=在控制台中键入'phil.followers'

Traceback (most recent call last):
  File "<console>", line 1, in <module>
AttributeError: 'User' object has no attribute 'followers'

我也许可以写一个函数？但我不完全确定我将编写什么来查询数据库，以获得所有跟踪某个特定用户的用户列表

Answer 1

我想出来了——其实很简单：

    def followers(self):
        return UserRelationship.query.filter_by(follows=self).all()