title: How can I customize the display of a model using contenttypes in the admin?
body: <p>I have these models:</p>
  
  <pre><code>class App(models.Model):
    name = models.CharField(max_length=100)
  
  class ProjectA(models.Model):
    name = models.CharField(max_length=100)
    app  = models.ForeignKey(App)
  
  class ProjectB(ProjectA):
    pass
  
  class Attachment(models.Model):
    content_type    = models.ForeignKey(ContentType)
    object_id       = models.PositiveIntegerField()
    project         = generic.GenericForeignKey("content_type","object_id")
    file            = models.FileField(upload_to=".")
  </code></pre>
  
  <p>I'm registering all the models for the admin, and I'm unregistering Group, User and Site. The thing is, when I access the Attachment in the admin, I see it rendered like this:</p>
  
  <p><img src="https://i.stack.imgur.com/iupHl.png" alt="admin for attachment"></p>
  
  <p>In the Content type select, I see this list:</p>
  
  <p><img src="https://i.stack.imgur.com/2eD6x.png" alt="select"></p>
  
  <p>The reason Attachment has a GenericForeignKey is because both ProjectA and ProjectB need to access it. I know that ProjectA and ProjectB are identical, but it's a requirement that they are stored in 2 separate tables. How could I made the Attachment class useable from the admin? I know how to use contenttypes from normal views, but from the admin not.</p>
  
  <p>In the Attachment class I would only like to have a select for Project A or Project B, and then a list of all Project A's or all Project B's, followed by the file that I want to attach.</p>
  
  <p>Is such a thing possible from the Admin? Will I need to show the user the Object Id column?</p>