title: Trying to filter based upon a value in another table
body: <p>I have 2 tables as</p>
  
  <pre><code>class ItemFollowers(models.Model):
      item = models.ForeignKey(Items, models.DO_NOTHING, db_column='item')
      user = models.ForeignKey(AuthUser, models.DO_NOTHING, db_column='user')
  </code></pre>
  
  <p>And the other one is</p>
  
  <pre><code>class UsrPosts(models.Model):
      item = models.ForeignKey('Items', models.DO_NOTHING, db_column='item')
      # Some other fields
  </code></pre>
  
  <p>How can I select the <code>UsrPosts</code> related to the <code>items</code> followed by some <code>user</code>? i.e. I can have records in <code>ItemFollowers</code> like (item0, user0), (item1, user0), (item5, user0). I need to filter <code>UsrPosts</code> based upon the user (aka. <code>request.user.id</code>)</p>
  
  <p>Here is a inefficient non-working way to get <code>UsrPostts</code></p>
  
  <pre><code>itms = ItemFollowers.objects.filter(user_id=request.user.id)
  qry = Q(item_id=itms[0].item.id) | ..... | Q(item_id=itms[N].item.id)
  posts = UsrPosts.objects.filter(qry)
  </code></pre>
  
  <p>Is there some filter magic to get it in one transaction?</p>