title: Django: UserProfile with Unique Foreign Key in Django Admin
body: <p>I have extended Django's User Model using a custom user profile called <code>UserExtension</code>.
  It is related to User through a unique ForeignKey Relationship, which enables me to edit it in the admin in an inline form!
  I'm using a signal to create a new profile for every new user:</p>
  
  <pre><code>def create_user_profile(sender, instance, created, **kwargs):  
      if created:
          try:  
              profile, created = UserExtension.objects.get_or_create(user=instance)
          except:
              pass  
  
  post_save.connect(create_user_profile, sender=User) 
  </code></pre>
  
  <p>(as described here for example: <a href="https://stackoverflow.com/questions/44109/extending-the-user-model-with-custom-fields-in-django">Extending the User model with custom fields in Django</a>)
  The problem is, that, if I create a new user through the admin, I get an IntegritiyError on saving "column user_id is not unique". It doesnt seem that the signal is called twice, but i guess the admin is trying to save the profile AFTERWARDS?
  But I need the creation through signal if I create a new user in other parts of the system!</p>