title: Relationships among these models in Django
body: <p>I want to build a website where:</p>
  
  <ul>
  <li>there is a set of 10 Cards</li>
  <li>on each Card, there are Important/Not_Important/Unknown attributes</li>
  <li>each User chooses which card are important and not important (from the same set of 10 Cards)</li>
  <li>his choices are saved and linked to his account.</li>
  </ul>
  
  <p>I have come up with models like these:</p>
  
  <ol>
  <li>User: I use <code>django.contrib.auth.models.User</code></li>
  <li><p>Card: </p>
  
  <pre><code>class Card(models.Model):
      is_important = models.NullBooleanField(default=None)
  </code></pre></li>
  <li><p>CardSet:</p>
  
  <pre><code>class CardSet(models.Model):
  
      cards = models.ManyToManyField(Card)
  
      user = models.ForeignKey(User,related_name='card_set')
  </code></pre></li>
  </ol>
  
  <p>It is obvious to me this database relationship has something wrong because, I don't know how to retrieve a list of cards that an instance of User has decided to be important/not important/unknown. However, I don't know how to put them in right relationship.</p>