title: Django admin change form load quite slow
body: <p>One of my Django websites has following database models:
  In Django App “common”:</p>
  
  <pre><code>class Collection(models.Model):
      name = models.CharField(max_length = 255, unique = True)
      _short_name = models.CharField(db_column="short_name", max_length = 32, blank=True)
  
  class Particle(models.Model):
      content = models.TextField(blank=False)
      owner = models.ForeignKey(Collection)
      order = models.IntegerField(null=True, blank=True)
  </code></pre>
  
  <p>In Django App “sitcom”:</p>
  
  <pre><code>class Media(models.Model):
      name = models.CharField(max_length = 248)
      _short_name = models.CharField(db_column="short_name", max_length = 32, blank=True)
      capital = models.CharField(max_length = 1)
      description = models.TextField(blank=True)
      progress = models.CharField(max_length = 32, blank=True, null=True)
  
  class Relation(models.Model):
      name = models.CharField(max_length = 128)
      _short_name = models.CharField(db_column="short_name", max_length = 32, blank=True)
      description = models.TextField(blank=True)
      parent = models.ForeignKey('self', blank=True, null=True)
      order = models.IntegerField(blank=True, null=True)
      particle = models.ForeignKey(Particle, blank=True, null=True)
      media = models.ForeignKey(Media, blank=True, null=True)
  </code></pre>
  
  <p>In short, model class Relation has 3 foreign keys to other tables. 
  The problem is, when I use Django Admin to change a single Relation, the page (change_form) loads rather slowly.
  Later, I changed model class Relation as following:</p>
  
  <pre><code>class Relation(models.Model):
      name = models.CharField(max_length = 128)
      _short_name = models.CharField(db_column="short_name", max_length = 32, blank=True)
      description = models.TextField(blank=True)
      order = models.IntegerField(blank=True, null=True)
      parent_id = models.IntegerField(blank=True, null=True)
      particle_id = models.IntegerField(blank=True, null=True)
      media_id = models.IntegerField(blank=True, null=True)
  </code></pre>
  
  <p>The modification changed Foreign Keys to IntegerFields, so it disabled some of the magics inside Django ORM system, and now the change form page loads really fast.
  My question is, what is the “disabled magics inside django orm”?  what has the potential to cause the problem?</p>