How/When does Django calculate the ForeignKey object

Question

I have a models class class A(models.Model): user = models.ForeignKey(User)

Now if I do a a = A.objects.get(pk = something_existing); print a.__dict__, user is not in __dict__. a.user however doesnot give an attribute error.

So when is the actual user being calculated? I looked in django.db.models.base.Model and django.db.models.base.ModelBase classes and they do not override __getattr__, (which I guessed might be being done), so where is this calculated/populated.

Answer 1

Django relation fields are implemented as descriptors.