On May 23, 2012, at 12:10 AM, ThereMichael wrote:
> I have this relation:
>
> # Users
> user_table = Table('user', self.metadata,
> Column('id', Integer, primary_key=True),
> Column('place_id', Integer),
> mysql_engine='InnoDB'
> )
>
> # Places
> places_table = Table('places', self.metadata,
> Column('id', Integer, primary_key=True),
> mysql_engine='InnoDB'
> )
>
> mapper(User, user_table,properties={
> 'user' : relation(Place,
> primaryjoin=(user_table.c.place_id==places_table.c.id),
> foreign_keys=[places_table.c.id]),
> }
> )
>
>
> mapper(Place, places_table, properties={
> 'id':places_table.c.id,
> }
> )
>
> A Place can be associated with multiple users.
That would make user.place_id the foreign key here. Put a ForeignKey() on the
"user.place_id" Column pointing to "places.id" and lose the foreign_keys
directive in the relation(). Because you have the primary key set as the FK
at the moment, detaching a user/place means the "foreign" column becomes null -
which if you've told it "places.id", means it's nulling out the primary key.
>
> I fetch a user as so:
>
> query = session.query(User).options(
> eagerload('place')).\
> filter_by(id=id)
>
> user = query.one()
>
> If there's a place associated with the user I end up with : user.place[],
> where user.place[0] is the first place, etc.
>
> Now, I want to remove the relation between this User and this Place, without
> deleting the place. So, I tried:
>
> user.place_id = None
>
> That fails with "AssertionError: Dependency rule tried to blank-out primary
> key column 'places.id' on instance '<Place at 0x1116df6d0>'"
>
> So, then I tried:
>
> del user.place[0]
>
> That fails also. I've also tried the various incarnations of
> passive_deletes=True and False (fails).
>
>
> The only solution I've come up with is this:
>
> session.expunge(user.place[0])
> user.place_id = None
>
> That works, but it doesn't feel right. Is there a better way? Thanks!
>
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