Question

Say I have the following models:

class Baz(models.Model):
    winning = models.CharField(max_length=100)

class Bar(models.Model):
    baz = models.ForeignKey(Baz)

class Foo(models.Model):
    bar = models.ForeignKey(Bar)

Now I have an instance of Foo, foo. How many queries does the following line execute?

winning = foo.bar.baz.winning

Does it do one for each foreign-key ., or is Django smart enough to only do one query here?

Answer 1

That will require 3 queries.

One to get foo, bar, and baz.

Use select_related() to get them at once.

Foo.objects.get(id=1).select_related('bar__baz__winning')