title: Django onetoonefield not saving instance
body: <p>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:</p>
  
  <pre><code>class ABLink(models.Model):
      a = models.OneToOneField(A, null=True)
      b = models.OneToOneField(B, null=True)
  </code></pre>
  
  <p>I use Django's post_save signal for model A to do the link:</p>
  
  <pre><code>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()
  </code></pre>
  
  <p>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</p>