Django annotate query set with a count on subquery

Question

This doesn\'t seem to work in django 1.1 (I believe this will require a subquery, therefore comes the title)

qs.annotate(interest_level= \\
             Count(Q(         


        

Answer 1

If you want to avoid dropping to raw SQL, another way to skin this cat would be to use a model method, which will then give you a new attribute on the model to use in your templates. Untested, but something like this on your Tags model should work:

class Tag(models.Model):
    itemfk = models.ForeignKey(Item, related_name='tags')
    name = models.CharField(max_length=32)

    def get_favetag_count(self):
        """
        Calculate the number of times the current user has favorited a particular tag
        """

        favetag_count = FavoritedTag.objects.filter(tag=self,user=request.user).count()
        return favetag_count

Then in your template you can use something like :

{{tag}} ({{tag.get_favetag_count}})

The downside of this approach is that it could hit the database more if you're in a big loop or something. But in general it works well and gets around the inability of annotate to do queries on related models. And avoids having to use raw SQL.