title: Getting a "The following content types are stale and need to be deleted" when trying to do a migrate. What does this mean, and how can I solve it?
body: <p>This is my models.py:</p>
  
  <pre><code>class Notification(models.Model):
      user = models.ForeignKey(User)
      createdAt = models.DateTimeField(auto_now_add=True, blank=True)
      read = models.BooleanField(default=False, blank=True)
  
      class Meta:
          abstract = True
  
  class RegularNotification(Notification):
      message = models.CharField(max_length=150)
      link = models.CharField(max_length=100)
  
  class FNotification(Notification):
      # same as Notification
      pass
  </code></pre>
  
  <p>When I do <code>python manage.py makemigrations</code>, this is what it says:</p>
  
  <pre><code>Migrations for 'CApp':
    0019_auto_20151202_2228.py:
      - Create model RegularNotification
      - Create model FNotification
      - Remove field user from notification
      - Add field f_request to userextended
      - Delete model Notification
  </code></pre>
  
  <p>First, it's weird that it says <code>Remove field user from notification</code> because <code>user</code> is still in my <code>Notiication</code> model (so if anyone can figure out why it says that it say 'removing the field user from notification', that would be great!) but nonetheless, when I move on and try to do <code>python manage.py migrate</code> I get this message:</p>
  
  <pre><code>Applying CMApp.0019_auto_20151202_2228... OK
  The following content types are stale and need to be deleted:
  
      CApp | notification
  
  Any objects related to these content types by a foreign key will also
  be deleted. Are you sure you want to delete these content types?
  If you're unsure, answer 'no'.
  
      Type 'yes' to continue, or 'no' to cancel: no
  </code></pre>
  
  <p>I typed <code>no</code>. But what exactly does this mean, why am I getting this message and how do I make it so that I don't require this message?</p>