Bug when saving an object pointed by another

[msbrogli@…]

My models are:

class A(models.Model):
    b = models.ForeignKey('B', null=True)
    name = models.CharField(max_length=255)

class B(models.Model):
    name = models.CharField(max_length=255)

The following code reproduces the problem:

a = A(name="Test A")
a.b = B(name="Test B")

a.b.save()
a.save()

a = A.objects.get(id=a.id)
assert a.b is not None

The assert fails! As I look inside the code, the field b_id is set only when a.b is being set. So, the workaround is:

a = A(name="Test A")
a.b = B(name="Test B")

a.b.save()
a.b = a.b  # workaround
a.save()

a = A.objects.get(id=a.id)
assert a.b is not None

Now it works as expected.

Is it a bug or a feature? I can't find anything in the docs.

If it is a bug, I guess the object should have a list of which objects are pointing to it. So, when it is added, it should updated everyone id field.

[Tim Graham]

Duplicate of #10811