Question

I have these models:

class A(Model):
pass

class B(Model):
the_a = ForeignKey(A)

class C(Model):
the_b = ForeignKey(B)

somewhere in code, I have an A instance. I know how to get all of the B’s associated with A; A.b_set.all() – but is there a way to get all of the C’s associated with all the B’s associated with my A, without doing potentially many queries?

Answer 1

You can execute this query to get all the C’s associated via B’s to your A:

C.objects.filter(the_b__the_a=instance_of_a)

where instance_of_a is some instance of class A.

For more information, see http://docs.djangoproject.com/en/dev/topics/db/queries/#lookups-that-span-relationships