title: python django implementing subscribers
body: <p>I have a very simple web application. A student comes in and he creates a note in one of the subjects. Each subject has number of subscribers. Similar to stackoverflow tags, once a tag has been added to a question, the subscribers are notified. </p>
  
  <p>Similary in my app, I want to add subscribers, so once a note is created for a particular subject, all the subscribers of that subject are mailed. </p>
  
  <p>I have my db models as follows - </p>
  
  <pre><code>class Subject(models.Model):
  //some vlaues here 
  
  class Note(models.Model):
      title = models.CharField(max_length=200)
      description = models.TextField()
      author = models.ForeignKey(User)
      subject = models.ForeignKey(Subject)
  
  class SubscriptionModel(models.Model):
      subject = models.ForeignKey(Subject)
      subscriber = models.ForeignKey(User)
  </code></pre>
  
  <p>There are couple of ways of implementing it - </p>
  
  <ol>
  <li><p>Once a note is created, a post_save signal can be fired to email all the subscribers of that subjecct. </p></li>
  <li><p>Something with pub-sub can be done. </p></li>
  <li><p>Something with rss feeds can be done. </p></li>
  </ol>
  
  <p>I am not sure what is a scalable approach to implement it, any help or pointers would be appreciated, thanks.</p>