如何創建模型的用戶關係多對多在SQLAlchemy的（蟒蛇，瓶），以自身

我需要創建一個表名爲朋友，它應該是這樣的：如何創建模型的用戶關係多對多在SQLAlchemy的（蟒蛇，瓶），以自身

朋友：

user_id說明
friend_id

我試圖從SQL教程要做到這一點鍊金術，但我還沒有找到如何在同一張桌子上建立多對多的關係。

這是我曾嘗試：

# friends table 
# many to many - user - user 
_friends = db.Table('friends', 
    db.Column('user_id', db.Integer, db.ForeignKey('users.id')), 
    db.Column('friend_id', db.Integer, db.ForeignKey('users.id')) 
) 


class User(db.Model, UserMixin): 

    # table name in database 
    __tablename__ = 'users' 

    # primary key for table in db 
    id = db.Column(db.Integer, primary_key=True) 

    # email is unique! 
    email = db.Column(db.String(255), unique=True) 

    # password, max = 255 
    password = db.Column(db.String(255)) 

    # category relation 
    categories = relationship("Category") 

    # cards relation 
    cards = relationship("BusinessCard") 

    # friends 
    friends = db.relationship(
     'User', 
     backref="users", 
     secondary=_friends 
    )

它說：

AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship User.friends - there are multiple foreign key paths linking the tables via secondary table 'friends'. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference from the secondary table to each of the parent and child tables.

沒有人知道該怎麼做是否正確？

來源

2014-01-17 Vasyl Romanchak