title: Django admin update of form fields based on foreign key model selection
body: <p>In django admin I have Model A with a foreign key association to Model B. Model B's values change based on the value of Model A. </p>
  
  <p>When a Model B object is selected for association with a Model A object, I would like to immediately display updated values for Model B based on the current value of Model A.</p>
  
  <p>I know that I can override the on_save method in the form to update the values when the user saves the form to the database. However, I would like the admin view to display the values before the user hits save.</p>
  
  <p>What do I need to hook into to make this update happen?</p>
  
  <p>Thank You</p>