title: How to .update m2m field in django
body: <p>I have:</p>
  
  <pre><code>class MyUser(Model):
      today_ref_viewed_ips = ManyToManyField(
          UniqAddress, 
          related_name='today_viewed_users', 
          verbose_name="Adresses visited referal link today")
      ...
  </code></pre>
  
  <p>On some croned daily request I do:</p>
  
  <pre><code>for u in MyUser.objects.all():
      u.today_ref_viewed_ips.clear()
  </code></pre>
  
  <p>Can it be done on DB server with update?</p>
  
  <pre><code>MyUser.objects.all().update(...)
  </code></pre>
  
  <hr>
  
  <p>Ok, I can't update, thanks. But only thing I need is to TRUNCATE m2m internal table, is it possible to perform from django? How to know it's name whithout  mysql's console "SHOW TABLES"?</p>