title: Is it possible to add a datetime column to a manytomany field?
body: <p>I was wondering if there was a way to add a datetime auto_now_add=True column to a manytomany field.
  I have the following model.</p>
  
  <pre><code>class Photographer(models.Model):
       user = models.OneToOneField(User, primary_key=True)
       bio = models.CharField(max_length=140, blank=True)
       favorites = models.ManyToManyField('Photo', through='Favorites', related_name = 'photographer_favs')
       likes = models.ManyToManyField('Photo', related_name='likedby', blank=True)
  </code></pre>
  
  <p>In my postgresql database, I have a separate table for likes called "djangoapp_<em>photographer</em>_likes".</p>
  
  <p>In this table, I have three columns:</p>
  
  <pre><code>id                 photographer_id        photo_id
  [PK] serial        integer                integer
      1                  3                    6
      2                  3                    7
      3                  3                    8
  </code></pre>
  
  <p>After several months of going into production, I realized that I would require the datetime of when these photos we're liked. So instead of three columns I would have four:</p>
  
  <pre><code>    id             photographer_id        photo_id      liked
  [PK] serial        integer                integer       timestamp with time zone
      1                  3                    6           2013-07-10 23:30:19.559463+00
      2                  3                    7           2013-07-11 17:00:53.39614+00
      3                  3                    8           2013-07-11 17:25:28.4953+00
  </code></pre>
  
  <p>Is it possible to add this extra column even though it is not in the models? I want it so that every time a picture is liked, the time at which it is liked is recorded. If this is not possible, what other work arounds should I look into?</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>This is my Photo model:</p>
  
  <pre><code>class Photo(models.Model):
       title = models.CharField(max_length=40, blank=True)
       photographer = models.ForeignKey(Photographer, related_name = 'shot_owner')
       postTime = models.DateTimeField(auto_now_add=True)
       description = models.CharField(max_length=255, blank=True)
       url = models.CharField(max_length=128)
  </code></pre>