On Jan 11, 2008 7:57 PM, Jonathan LaCour <[EMAIL PROTECTED]> wrote:
>
> Jonathan LaCour wrote:
>
> >> I am attempting to model a doubly-linked list, as follows:
> >
> > ... seems to do the trick. I had tried using backref's earlier,
> > but it was failing because I was specifying a "remote_side"
> > keyword argument to the backref(), which was making it blow up
> > with cycle detection exceptions for some reason.
>
> Oops, spoke too soon! Here is a test case which shows something
> quite odd. I create some elements, link them together, and then
> walk the relations forward and backward, printing out the results.
> All seems fine. Then, I update the order of the linked list, and
> print them out forward, and they work okay, but when I print things
> out in reverse order, its all screwy.
>
> Any ideas?
I believe you need either the only next_task_id or the only
previous_task_id, but not both, since one can be calculated from
another. Something like the following:
task_table = Table('task', metadata,
Column('id', Integer, primary_key=True),
Column('name', Unicode),
Column('next_task_id', Integer, unique=True, ForeignKey('task.id')),
)
Session.mapper(Task, task_table, properties={
'next_task' : relation(
Task,
uselist=False,
remote_side=task_table.c.id,
backref=backref('previous_task', uselist=False),
),
})
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