title: Django filter the model on ManyToMany count?
body: <p>Suppose I have something like this in my models.py:</p>
  
  <pre><code>class Hipster(models.Model):
    name = CharField(max_length=50)
  
  class Party(models.Model):
    organiser = models.ForeignKey()
    participants = models.ManyToManyField(Profile, related_name="participants")
  </code></pre>
  
  <p>Now in my views.py I would like to do a query which would fetch a party for the user where there are more than 0 participants. </p>
  
  <p>Something like this maybe:</p>
  
  <pre><code>user = Hipster.get(pk=1) 
  hip_parties = Party.objects.filter(organiser=user, len(participants) &gt; 0)
  </code></pre>
  
  <p>What's the best way of doing it? </p>