class A(models.Model):
    text = models.TextField(blank=True)

class B(models.Model):
    a = models.ForeignKey(a, related_name="foo")
    text = models.TextField(blank=True)

>>> x = A(1)
>>> y = B(a=x, bar=1)
>>> x
<A: A object>
>>> y
<B: B object>
>>> x.__dict__
{'foo': 0, '_state': <django.db.models.base.ModelState object at 0x3772d10>, 'id': 1}
>>> y.__dict__
{'bar': 1, '_a_cache': <A: A object>, '_state':<django.db.models.base.ModelState object at 0x3772d90>, 'id': None, 'a_id': 1}