title: Django : Check object existance in ManytoManyField
body: <p>I have ChatRoom model as,</p>
  
  <pre><code>class ChatRoom(models.Model):
      name = models.CharField(max_length=300)
      owner = models.ForeignKey(UserProfile)
      description = models.CharField(max_length=300)
      members = models.ManyToManyField(UserProfile,related_name='members')
      members_requested = models.ManyToManyField(UserProfile,related_name='member_requested')
      members_blocked = models.ManyToManyField(UserProfile,related_name='member_blocked')
      def __unicode__(self):
          return self.name
  </code></pre>
  
  <p>For example I have added a UserProfile instances to members field. </p>
  
  <pre><code>chr_obj.members.add(up_obj1,up_obj2)
  </code></pre>
  
  <p>How can i check whether a UserProfile object is there or not. I tried with, 
  if <code>chr_obj.name ='new room'</code></p>
  
  <p>up_obj.chatroom_set.filter(name='new room').exists()</p>
  
  <p>but it returns false. How to verify that ?? 
  Thanks.</p>