title: Django admin - Limit the choices in dropdown
body: <p>I am now starting to use django and I have an issue trying to filter data based on user information. Let me explain how my app works. A User in my app belongs to a company. So I created a table called Company to capture company info. Then I created another table called UserCompany. Basically, it stores the Id from Django User and the Id from my company table. Now, I want to filter data that the user will see in Django Admin based on their company id. He/She can only see data based on their company Id. I was able to figure this user using <code>get_queryset</code> in admin.py. My only issue now is, the dropdown list that shows in admin as a result of foreign keys isn't being filtered. I did some research and found out about limit_choices_to. I can set that statically like this:</p>
  
  <pre><code>class Cleaner(models.Model):
      company = models.ForeignKey('Company',limit_choices_to = {'companyname' = 'Test'}
  </code></pre>
  
  <p>The dropdown list in admin section only shows the company Test. How can I do this dynamically? Do I do it in the model or do I do it in admin.py? Please help!!</p>