make those m2m relations(), and any other relation that doesn't represent
a single path of persistence, viewonly=True . its all the "three ways to
see the same thing" going on, minus viewonly=True means "three ways to
persist the same thing", leading to errors like that.
Kevin Dangoor wrote:
>
> I have a many-to-many mapping that joins against a single table. The
> relation works fine, except when I try to add a new mapping via the
> list created by relation(). To make things extra interesting, I'm
> using declarative (which I really like, actually, because it maps in a
> fairly straightforward manner to standard SA-isms). Here's the setup:
>
> class Connection(Base):
> __tablename__ = "connections"
> followed_id = Column(Integer, ForeignKey('users.id',
> ondelete='cascade'), primary_key=True)
> followed = relation('User',
> primaryjoin='User.id==Connection.followed_id')
>
> following_id = Column(Integer, ForeignKey('users.id',
> ondelete='cascade'), primary_key=True)
> following = relation('User',
> primaryjoin='User.id==Connection.following_id')
>
> followed_viewable = Column(Boolean, default=False)
>
> class User(Base):
> __tablename__ = "users"
>
> id = Column(Integer, primary_key=True)
> username = Column(String(128), unique=True)
> email = Column(String(128))
> password = Column(String(20))
> settings = Column(PickleType())
> projects = relation('Project', backref='owner')
> quota = Column(Integer, default=10)
> amount_used = Column(Integer, default=0)
>
> # this is the interesting part
> users_i_follow = association_proxy('i_follow', 'followed')
> i_follow = relation(Connection,
> primaryjoin=Connection.following_id==id,
> secondary=Connection.__table__,
> secondaryjoin=id==Connection.followed_id)
>
> users_following_me = association_proxy('following_me', 'following')
> following_me = relation(Connection,
> primaryjoin=Connection.followed_id==id,
> secondary=Connection.__table__,
> secondaryjoin=id==Connection.following_id)
>
> def follow(self, ou):
> self.i_follow.append(Connection(following=self, followed=ou))
>
> So, everything works just fine when I add the connection to the session:
>>>> u1 = User("kevin", "foo", "bar")
>>>> u2 = User("joe", "foo", "bar")
>>>> s.add(u1)
>>>> s.add(u2)
>>>> s.add(Connection(following=u1, followed=u2))
>>>> s.flush()
>>>> u1.users_i_follow
> [<bespin.model.User object at 0x78ee30>]
>>>> u1.i_follow
> [<bespin.model.Connection object at 0x7d0c10>]
>>>> u2.users_following_me
> [<bespin.model.User object at 0x78ed50>]
>
> But when I try to use that follow method defined up there, I get an
> exception:
>
> File
> "/Users/admin/projects/bespin/lib/python2.5/site-packages/sqlalchemy/orm/sync.py",
> line 81, in _raise_col_to_prop
> raise exc.UnmappedColumnError("Can't execute sync rule for source
> column '%s'; mapper '%s' does not map this column. Try using an
> explicit `foreign_keys` collection which does not include destination
> column '%s' (or use a viewonly=True relation)." % (source_column,
> source_mapper, dest_column))
> sqlalchemy.orm.exc.UnmappedColumnError: Can't execute sync rule for
> source column 'users.id'; mapper 'Mapper|Connection|connections' does
> not map this column. Try using an explicit `foreign_keys` collection
> which does not include destination column 'connections.followed_id'
> (or use a viewonly=True relation).
>
> users.id *is* mapped in Connection (twice, in fact, which may be the
> problem...) I'm hoping that there's some simple flag I'm missing
> here.
>
> Kevin
>
> --
> Kevin Dangoor
>
> work: http://labs.mozilla.com/
> email: k...@blazingthings.com
> blog: http://www.BlueSkyOnMars.com
>
> >
>
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