On Mon, Feb 23, 2009 at 12:40 PM, sphogan <spho...@gmail.com> wrote:
>
> I'm surprised that this hadn't come up for me before, but nonetheless,
> here I am.
>
> My problem is that I want to get related items (in a similar situation
> to getting blog articles with their comments) without looping a second
> lookup (since it would be a couple thousand items and building a page
> off a couple thousand queries isn't a good idea).
>
> Basically, the schema is like this:
>
> Article(models.Model):
> #fields for article
>
> Comment(models.Model):
> #fields for comment
> article = models.ForeignKey(Article)
>
> Simple enough. If I wanted to get all the comments and their related
> article, I could do:
>
> Comment.objects.select_related('article').all()
>
> However, select_related() only works on the object the foreign key is
> declared on (http://docs.djangoproject.com/en/dev/ref/models/querysets/
> #id4 <http://docs.djangoproject.com/en/dev/ref/models/querysets/%0A#id4>;
> specifically, "You can only refer to ForeignKey relations in the
> list of fields passed to select_related.") Presumably this is because
> it does an INNER JOIN rather than a LEFT OUTER JOIN and would
> therefore miss articles with no comments.
>
> What I would like to be able to do is:
>
> Article.objects.select_related('comment_set').all()
>
> This seems like a somewhat simple case and there seems to be no
> mention of it in the documentation anywhere.
>
> Sean.
>
> >
>
That's not possible, but that doesn't really affect anything, you still have
that accessor available to you, but it does an extra SQL query, that is to
say select_related does not affect the data avilable to you, it is a
performance optimization.
Alex
--
"I disapprove of what you say, but I will defend to the death your right to
say it." --Voltaire
"The people's good is the highest law."--Cicero
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