Implicitly save related models as needed instead of raising "unsaved related objects error" on Model.save()

[aki33524]

class Foo(models.Model):
  pass

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

>>> foo = Foo()
>>> bar = Bar(foo=foo)

-------------------------
>>> bar.save()
...
ValueError: save() prohibited to prevent data loss due to unsaved related object 'foo'.

-------------------------
>>> foo.save()
>>> bar.save()
IntegrityError: NOT NULL constraint failed: t26366_bar.foo_id

-------------------------
>>> foo.save()
>>> bar.foo = bar.foo
>>> bar.save() 
(no errors)

This is very odd behavior.

And, when implementing bar.save() without foo.save(), I wish Django implemented foo.save() implicitly.
Like QuerySet.delete(), ON DELETE CASCADE emulation.

[Tim Graham]

I don't think there's much justification for making a change in Django here. As noted in a related ticket, "Automatically saving related objects is too magic; I'm sure it would be considered unexpected and undesirable in some circumstances."

An alternate solution in your own code is:

bar.foo.save()
bar.save()