On Wed, Jun 17, 2009 at 10:00 AM, R C <rileycr...@gmail.com> wrote:
>
> Thanks for your fast reply....
>
> I realize that there is no "count" field in my article model. However
> in my templates I am able to do things like:
> Author.article_set.count
>
> I just can't do the same thing in my views when building a
> queryset.....I would really like to be able to select Authors and
> order them by the number of Articles they have written. Any ideas on
> how to accomplish this?
>
>
>
> One could accomplish this with SQL as follows:
> select author_id, count(author_id) from article_table group by
> author_id;
>
> This would return something like
> author_id | count(author_id)
> 1 10
> 2 20
> 3 30
>
> On Jun 17, 3:47 pm, Daniel Roseman <dan...@roseman.org.uk> wrote:
> > On Jun 17, 1:12 pm, R C <rileycr...@gmail.com> wrote:
> >
> >
> >
> > > Hi,
> >
> > > I would like to be able to select objects and order them by the count
> > > of a related field
> >
> > > For example, I have 2 models:
> >
> > > class Author(models.Model)
> > > name = models.Charfield(max_length=20)
> >
> > > class Article(models.Model)
> > > author = models.ForeignKey(Author)
> > > content = models.TextField()
> >
> > > Let's say I have 3 authors:
> > > 1) John -- has 10 articles
> > > 2) Bob -- has 20 articles
> > > 3) Lisa -- has 30 articles
> >
> > > I would like to select authors and order by the number of articles
> > > they have written:
> > > Author.objects.all().order_by('article__count')
> >
> > > But this does not work.
> >
> > No, because you don't have a 'count' field in your article model.
> >
> > Read this (SVN version only):
> http://docs.djangoproject.com/en/dev/topics/db/aggregation/
> > --
> > DR.
> >
>
That's why Daniel linked the aggregates documentation, which allows queries
such as the one you suggested to be preformed:
Author.objects.annotate(c=Count('article')).oder_by('c')
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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