Using Django ORM query How to annotate if multiple levels of foreign key hierarchy exists

Question

My Django models looks like

class Parent(models.Model):
    name = models.CharField(('name'), max_length=30)

class Child(models.Model):
    parent = models.ForeignKey(Parent)
    name = models.CharField(('name'), max_length=30)

class GrandChild(models.Model):
    child = models.ForeignKey(Child)
    name = models.CharField(('name'), max_length=30)

-> To Get Number of Childs for parent following query does               
    Parent.objects.annotate(childs=Count('Child')).values('childs')

-> To Get Number of Grand Childs for parent following query does               
    Parent.objects.annotate(childs=Count('child')).annotate(grandchilds=Count('child__grandchild'))

But how can I get the count of number of childs and number of grand childs for each parent

Answer 1

Try to use distinct:

Count('child', distinct=True)

More details by link:

https://docs.djangoproject.com/en/1.9/topics/db/aggregation/#combining-multiple-aggregations