title: Django ManyToManyField error
body: <p>I am using Django's ManyToManyField, and when i try to add data to it, i get the following error: </p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;console&gt;", line 1, in &lt;module&gt;
    File "/home/purav/Desktop/socmov/fbcon/models.py", line 165, in getMovieInfo
      movie.genre.add( G )
    File "/usr/local/lib/python2.6/dist-packages/django/db/models/fields/related.py", line 503, in add
      self._add_items(self.source_field_name, self.target_field_name, *objs)
    File "/usr/local/lib/python2.6/dist-packages/django/db/models/fields/related.py", line 563, in _add_items
      (obj, self.instance._state.db, obj._state.db))
  ValueError: Cannot add "&lt;Genre: Genre object&gt;": instance is on database "None", value is on database "default"
  </code></pre>
  
  <p>I am using Django 1.3, and i following is a part of my code:</p>
  
  <pre><code>class Genre(models.Model):
      gid = models.IntegerField(primary_key = True)
      name = models.CharField(max_length = 20)
  
  class Movie(models.Model):
      mid = models.IntegerField(primary_key = True)
      name = models.CharField(max_length = 100)
      genre = models.ManyToManyField("Genre")
  </code></pre>
  
  <p>This is where the error occurs:</p>
  
  <pre><code>G = Genre.objects.get(gid = obj[i]['id'])
  print G.name, G.gid
  movie.genre.add( G )
  </code></pre>
  
  <p>It is guaranteed that obj[i]['id'] will be found inside Genre. Can someone please help me?</p>