您所需要做的就是在表中添加primaryjoin，并在Friendship表中添加两个“ foreign_key”外键。您还需要与全班同学建立友谊。
class Friendship(db.Model): __tablename__ = 'friend' fk_user_from = db.Column(db.Integer, db.ForeignKey('user.id'), primary_key=True) fk_user_to = db.Column(db.Integer, db.ForeignKey('user.id'), primary_key=True) extra_field = db.Column(db.Integer)class User (db.Model): __tablename__ = 'user' id = db.Column(db.Integer, primary_key=True) user_to = db.relationship('Friendship',backref='to', primaryjoin=id==Friendship.fk_user_to) user_from = db.relationship('Friendship',backref='from', primaryjoin=id==Friendship.fk_user_from )要添加朋友，您需要定义“友谊”，例如：
friend = Friendship(extra_field=0 , to=me , from=my_friend)
