title: IntegrityError using Django's loaddata when switching to Postgres
body: <p>I am getting the following error:</p>
  
  <pre><code>IntegrityError: duplicate key value violates unique constraint "users_userprofile_pkey"
  </code></pre>
  
  <p>I am migrating from MySQL to Postgres, so I am dumping the data from the MySQL database using:</p>
  
  <pre><code>python2.7 manage.py dumpdata --indent=4 --natural &gt; dump.json
  </code></pre>
  
  <p>I get the error when I attempt to load the dump.json into the Postgresql database:</p>
  
  <pre><code> python manage.py loaddata dump.json
  </code></pre>
  
  <p>I have the following signals in my users/model:</p>
  
  <pre><code>post_save.connect(create_user_profile, sender=User, dispatch_uid="user_create_profile")
  post_save.connect(create_api_key, sender=User, dispatch_uid="user_create_api_key")
  </code></pre>