title: Django : join without related object
body: <p>I have two models in django :</p>
  
  <pre><code>class Matching(models.Model):
      representative_remote_id = models.CharField(max_length=200, null=True)
      representative_name = models.CharField(max_length=200)
      representative_group = models.CharField(max_length=200)
  
  
  class Vote(models.Model):
      representative_name = models.CharField(max_length=200, blank=True, null=True)
      representative_remote_id = models.CharField(max_length=200, blank=True, null=True)
      # ...
  </code></pre>
  
  <p>As you can see, there are no relation between these two models.
  What I want is select all votes where :</p>
  
  <pre><code>vote.representative_name = CONCAT(matching.mep_name, ' (', matching.mep_group, ')')
  AND matching.representative_remote_id IS NULL
  AND vote.representative_remote_id IS NOT NULL
  </code></pre>
  
  <p>I can’t find a way to do this with django (without using 'raw' sql query)</p>