On Aug 4, 2:09 am, Malcolm Tredinnick <malc...@pointy-stick.com>
wrote:
> On Mon, 2009-08-03 at 17:45 +0300, Shai Berger wrote:
> > Hi all,
>
> > With the new aggregates in django 1.1, I wonder if there's an easy way to
> > aggregate over reverse relationships. As an example, assume a simplistic
> > representation of a set of teams:
>
> > class Team(models.Model):
> > name = models.CharField(max_length=100)
>
> > class Player(moedls.Model):
> > name = models.CharField(max_length=100)
> > team = models.ForeignKey(Team)
>
> > Now, I want to perform some operation on all the empty teams -- so I want to
> > do something like
>
> > Team.objects.annotate(num_players=Count('player_set')).filter(num_players__eq=0)
>
> So what happened when you tried this? It looks like it should work and I
> use similar sorts of queries with success in existing code.
>
I am deeply surprised. I never thought reverse relationships worked so
smoothly.
The only problem with my version above is attempting to count the
player_set;
Count('player') works, as you said.
>
> Team.objects.filter(player=None)
>
And this indeed works too, and surprises me too, because Team does not
have a
player field.
Well. You learn interesting Django tidbits every day.
Thanks,
Shai.
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