Django conditional Subquery aggregate

Question

An simplified example of my model structure would be

class Corporation(models.Model):
    ...

class Division(models.Model):
    corporation = models.ForeignKey(         


        

Answer 1

You should be able to do this with a Case() expression to query the count of departments that have the type you are looking for:

from django.db.models import Case, IntegerField, Sum, When, Value

Corporation.objects.annotate(
    type_10_count=Sum(
        Case(
            When(division__department__type=10, then=Value(1)),
            default=Value(0),
            output_field=IntegerField()
        )
    )
)