Ah - yes, that is so awesome! For anyone interested, here's the magic
incantation:
Book.objects.annotate(Count('reader')).order_by('reader__count')
Or more verbosely:
Book.objects.annotate(num_readers=Count('reader')).order_by
('num_readers')
That documentation link describes it very well. Thanks Scott!
Margie
On Jan 11, 7:51 pm, Scott Maher <sc...@thereceptor.net> wrote:
> Margie Roginski wrote:
> > Say I have a Reader model that has a foreign key to a Book
>
> > class Reader(models.Model):
> > book = models.ForeignKey(Book)
>
> > Now say I want to find all books and order them by the number of
> > readers. Is that possible, ie something like this?
>
> > Book.objects.all().order_by(reader_set__count)
>
> > This syntax doesn't work, however. Is this possible?
>
> > Margie
>
> I can't give you specific code but I think that you want is under the
> Aggregation section of the documentation. Specifically I think you want
> to apply the Count object on the Book reader set. You were almost there. :)
>
> http://docs.djangoproject.com/en/dev/topics/db/aggregation/#topics-db...
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