Ok..thanks.. I was afraid I was going to get that answer. If I do
this with select_related, I'm still going to have to implement a loop
to display them all in one list, because they'd come back as
company.parent_company.parent_company etc, instead of all in one top
level list... right?
On Oct 8, 9:19 am, Malcolm Tredinnick <[EMAIL PROTECTED]>
wrote:
> On Mon, 2007-10-08 at 13:13 +0000, [EMAIL PROTECTED] wrote:
> > In my model class I have:
>
> > class Company(models.Model):
> > company_id = models.AutoField(primary_key=True)
> > parent_company = models.ForeignKey("self",null=True)
> > .
> > .
>
> > How would I query to get back all children companies, as well as all
> > of their children companies, and their children companies, etc,
> > without writing a nested loop to do so?
>
> You can't do it with a general query because there's no way to do it in
> SQL with this data structure. The SQL has to do a join each time you
> query from parent back to child (or vice-versa), so we need to know the
> number of joins to create a query construction time.
>
> There is a "depth" parameter for select_related() queries that limits
> the number of recursion steps (otherwise infinite loops would result for
> queries like this) and you could use that to control the maximum number
> of children. However, I believe there are some bugs with it working for
> small values of depth (depth=1) and there might be others, so check the
> results carefully.
>
> Regards,
> Malcolm
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