Foreign keys and IntegrityError: id may not be NULL

Django newbie here. I have two simple models like this:

class Fluff(models.Model):
    # ....
    # some fields definitions

class Something(models.Model):
    name = models.CharField(max_length=200)
    fluff = models.ForeignKey(Fluff)

syncdb goes as expected, and then I go to the shell to test things:

>>> s = Something()
>>> s.name = 'Blah'
>>> s.fluff = Fluff(...)
>>> s.save()
Traceback (most recent call last): # traceback skipped for brevity
IntegrityError: app_something.fluff_id may not be NULL

I expected Django to do its magic, figure out fluff is not saved, then save it before saving s. That didn't happen, but it's OK, I can sav开发者_如何学JAVAe fluff for myself, let's try again:

>>> s = Something()
>>> s.name = 'Blah'
>>> s.fluff = Fluff(...)
>>> s.fluff.save()
>>> s.save()
Traceback (most recent call last): # traceback skipped for brevity
IntegrityError: app_something.fluff_id may not be NULL

No luck. This should be trivial, but I cannot figure it out at the moment. Any help would be appreciated.

---

Try to do something like this:

>>> s.name = 'Blah'
>>> obj = Fluff(...)
>>> obj.save()
>>> s.fluff = obj
>>> s.save()