title: Django Adding Values to ForeignKey
body: <p>I'm trying to set up a way for users to "watch" certain items (i.e. add items to a list containing other items by other users):</p>
  
  <pre><code>class WatchList(models.Model):
      user = models.ForeignKey(User)
  
  class Thing(models.Model):
      watchlist = models.ForeignKey(WatchList, null=True, blank=True)
  </code></pre>
  
  <p>How do I add a <code>Thing</code> to a users <code>WatchList</code>?</p>
  
  <pre><code>&gt;&gt;&gt; from myapp.models import Thing
  &gt;&gt;&gt; z = get_object_or_404(Thing, pk=1)
  &gt;&gt;&gt; a = z.watchlist.add(user="SomeUser")
  
    AttributeError: 'NoneType' object has no attribute 'add'
  </code></pre>
  
  <p>How can I add the item to the watchlist? And/or is this the appropriate way to set up my model fields? Thanks for any ideas!</p>