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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