问题描述

学习《flask web开发》中多对多关系时时遇到问题

 class Follow(db.Model):    __tablename__ = 'follows'    follower_id = db.Column(db.Integer db.ForeignKey('users.id')                            primary_key=True)    followed_id = db.Column(db.Integer db.ForeignKey('users.id')                            primary_key=True)    timestamp = db.Column(db.DateTime default=datetime.utcnow)class User(UserMixin db.Model):    __tablename__ = 'users'    id = db.Column(db.Integer primary_key=True)    email = db.Column(db.String(64) unique=True index=True)    username = db.Column(db.String(64) unique=True index=True)    password_hash = db.Column(db.String(128))    confirmed = db.Column(db.Boolean default=False)    name = db.Column(db.String(64))    location = db.Column(db.String(64))    about_me = db.Column(db.Text())    #头像哈希    avatar_hash = db.Column(db.String(32))    posts = db.relationship('Post' backref='author' lazy='dynamic')    followed = db.relationship('Follow'                               foreign_keys=[Follow.follower_id]                               backref=db.backref('follower' lazy='joined')                               lazy='dynamic'                               cascade='all delete-orphan')    followers = db.relationship('Follow'                                foreign_keys=[Follow.followed_id]                                backref=db.backref('followed' lazy='joined')                                lazy='dynamic'                                cascade='all delete-orphan')

这里，User的followed的外键指定为Follow.follower_id 的意思是不是 ，该User对象的id对应的是followed中Follow对象中的follower_id 。这样理解有没有问题？还有其他参数都是什么意思？