title: Django - Model field for user groups
body: <p>I have model called <code>PM</code> to create <code>Private Message objects</code>. which is:</p>
  
  <pre><code>class Pm(models.Model):
  
      """
      Messaging System
      """
      subject = models.CharField(verbose_name='Message Subject',
                                 max_length=50, blank=False)
      content = models.TextField(verbose_name='Message Content',
                                 max_length=1000, blank=False)
      to = models.ForeignKey(settings.AUTH_USER_MODEL, null=False,
                             blank=False,verbose_name='Target',
                             related_name='target')
      sender = models.ForeignKey(settings.AUTH_USER_MODEL,
                                 blank=False,verbose_name='Sender',
                                 null=False,
                                 related_name='source')
  </code></pre>
  
  <p>i can create a message to single user. If i change <code>to</code> field into a <code>Many2Many</code> field, then i can create this message for multiple users.</p>
  
  <p>But what i want is to create this message for some user groups. There should be a group like <code>Programmers</code> which includes 10 users.</p>
  
  <p>I am using <code>Django Admin</code> to manage this.</p>
  
  <p>thanks</p>