annotate() and aggregate() for generically-related data. also a handy function for filtering GFK-model querysets.
Use django's GenericRelation where possible, as this can make the queries generated more efficient by using a JOIN rather than a subquery.
# install from pypi
pip install django-generic-aggregation
# or install via git
pip install -e git+git://github.com/coleifer/django-generic-aggregation.git#egg=generic_aggregation
The examples below assume the following simple models:
class Rating(models.Model):
rating = models.IntegerField()
object_id = models.IntegerField()
content_type = models.ForeignKey(ContentType)
content_object = GenericForeignKey(ct_field='content_type', fk_field='object_id')
class Food(models.Model):
name = models.CharField(max_length=50)
ratings = generic.GenericRelation(Rating) # reverse generic relation
You want to figure out which items are highest rated (generic_annotate)
from django.db.models import Avg
food_qs = Food.objects.filter(name__startswith='a')
generic_annotate(food_qs, Rating, Avg('ratings__rating'))
# you can mix and match queryset / model
generic_annotate(food_qs, Rating.objects.all(), Avg('ratings__rating'))
You want the average rating for all foods that start with 'a' (generic_aggregate)
food_qs = Food.objects.filter(name__startswith='a')
generic_aggregate(food_qs, Rating, Avg('ratings__rating'))
You want to only display ratings for foods that start with 'a' (generic_filter)
food_qs = Food.objects.filter(name__startswith='a') generic_filter(Rating.objects.all(), food_qs)