title: Subclassing AbstractUser in Django for two types of users
body: <p>I'm developing a school database system in Django 1.5, and was planning on having a number of different user types (Student, Staff, Parent) which subclass AbstractUser (actually, another abstract subclass of AbstractUser). I was just attempting to add an externally developed app to my system, which uses User in a ForeignKey for some of its models, however, this fails as my user type is not a 'User' instance. I can't set the apps models to use AbstractUser as one can't use abstract classes for Foreign Keys. I was then considering adding to my settings.py <code>AUTH_USER_MODEL = 'myapp.MyUser'</code> and using settings.AUTH_USER_MODEL in place of User for the ForeignKey in the app. However, I have 3 different user types, so can't do this either.</p>
  
  <p>An earlier prototype used Django 1.4, which did not support custom User models, hence had a reference to a User instead, but this required an extra join for every query, which was leading to quite complex queries. Is this the only way I can go forward with this, or is there another solution?</p>