[sqlalchemy] single table inheritance + composite primary key problem

[Vladimir Iliev]

hi,

what's wrong with the following mapping ?

TYPE_DEFAULT = 1

class BaseFriend(DeclarativeBase):
    
    __tablename__ = 'friends'
    __table_args__ = {'mysql_engine': 'InnoDB',
                      'mysql_charset': 'utf8'}
    
    type = Column(SmallInteger, primary_key=True)

    user_id = Column(None, ForeignKey('users.id', ondelete='CASCADE'), 
primary_key=True)
    
    friend_id = Column(None, ForeignKey('users.id', ondelete='CASCADE'))

    friend_external_id = Column(String(100), primary_key=True)

    __mapper_args__ = dict(
        polymorphic_on=type,
        polymorphic_identity=TYPE_DEFAULT,
    )

TYPE_FACEBOOK = 2

class FacebookFriend(BaseFriend):
    
    __mapper_args__ = dict(
        polymorphic_identity=TYPE_FACEBOOK,
    )

User.facebook_friends = relationship(FacebookFriend,
    lazy=False,
    primaryjoin=FacebookFriend.user_id==User.id,
    backref='user'
)

when i try to session.query(User).first() i'm getting:

New instance <FacebookFriend at 0x5b79850> with identity key (<class 
'...Friend.BaseFriend'>, (2, 75L, u'100001288076626')) conflicts with 
persistent instance <FacebookFriend at 0x5c59710>

i've tried to define the relationship on both sides with the same results

thanks

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