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

[Vladimir Iliev]

p.s. i'm using SA 0.7.1

[Michael Bayer]

Two friends with the same identity key, that is, associated with the same type, user_id (and hence User object), and friend_external_id.

I'm not sure what friend_external_id is but if it just refers to some outside source, I doubt you want want the "user_id" column to be part of the primary key here, that establishes one-to-one, not one-to-many.

[Vladimir Iliev]

what i need is friend model with pk (facebook, user id (multiple users might have same external id as friend so it must be part of the key), and friend external id (which in this case is facebook uid)) ... i can probably just use autoincrement integer for primary key but there would be millions friend rows and i prefer if it's tiny. i'm adding and deleting FacebookFriend objects without problems but it fails when i try to session.query(User) with facebook_friends eagerloaded or session.merge(user) if user is loaded from memcached