Django: how to annotate queryset with count of filtered ForeignKey field?

Question

Django novice question :)

I have the following models - each review is for a product, and each product has a department:

class Department(models.Mod         


        

Answer 1

In django >= 2.0 this could be achieved with

depts = Department.objects.all().annotate(
    num_products=Count('product', filter=Q(product__review__time__range=["2012-01-01", "2012-01-08"]))
)

For more info read docs https://docs.djangoproject.com/en/2.0/topics/db/aggregation/#filtering-on-annotations