title: Filter a reverse manytomany django in one line?
body: <p>these are my models.</p>
  
  <pre><code>class League(models.Model):
      league_name=models.CharField(max_length=20)
      league_id=models.IntegerField()
  
  class LeagueAdministrator(models.Model):
      administrator = models.ManyToManyField(User)
      league = models.ManyToManyField('League')
  </code></pre>
  
  <p>Given that there can be more than one administrators for league: I want a single query which returns a query set with all the user objects who are administator of a specific league. This is what I do now.</p>
  
  <pre><code>league=League.objects.get(league_id=1)
  usersids=LeagueAdministrator.objects.filter(league=league).values_list('administrator')
  Administrators=User.objects.filter(id__in=usersids)
  </code></pre>
  
  <p>Thank you.</p>