user2959723 user2959723 - 4 months ago 42
Python Question

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

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

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

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