Django onetoonefield not saving instance

Question

I am working on an application where i have two models for the purpose of this question let's call them A and B. I want to have another model where I 'link' both A and B just to make it easy for me to find the instance of B that relates to A. So I came up with:

class ABLink(models.Model):
    a = models.OneToOneField(A, null=True)
    b = models.OneToOneField(B, null=True)

I use Django's post_save signal for model A to do the link:

mashup, cr = ABLink.objects.get_or_create(a=instance)
if cr:
     mashup.b = B()
else:
    if mashup.b is None:
        mashup.b = B()
.... (assign values to mashup.b attributes)
mashup.b.save()
mashup.save()

The problem is mashup.b is never saved in the DB. On checking in phpMyAdmin b is set to NULL. Any idea what I may be doing wrong

Answer 1

At first create B instance, assign attributes to it, call save on it (now it have id) and then assign it to mashup.b:

if cr:
     b = B()
else:
    if mashup.b is None:
        b = B()

#.... (assign values to b attributes)

b.save()
mashup.b = b
mashup.save()