title: Django saving to ManyToMany fields
body: <p>I have a simple model class with 2 ManyToManyField fields like this:</p>
  
  <p><strong>models.py</strong></p>
  
  <pre><code>class Folder(models.Model):
      user = models.ManyToManyField(User)
      asset = models.ManyToManyField(Asset)
  </code></pre>
  
  <p>In my view, I know the user ID and the asset ID.  Say the user ID is 1 and the asset ID is 30, how do I inject this row?  I guess I don't understand how to instantiate Folder so I can save/update the row.</p>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def addAssetToMyFolder(request, id=None):
      ''' view is simplified for brevity
      '''
      f = Folder(
          user = 1,
          asset = 30,
      )
      f.save()
  </code></pre>