code: def update(self):
          
          #get the raw data
  #        self.posts.all().delete() # TODO: handle in update_posts if source changes without deleting every time
          data = self._get_data()
          #iterate through them and for each item
          msg = []
          for entry in data:
              link = self._get_entry_link(entry)
              stored_entry, is_new = Post.objects.get_or_create(link=link)
              self._store_post(stored_entry, entry)
              if is_new is True:
              #self._set_dates(stored_entry)
              #                self._store_post(stored_entry, entry)
                  msg.append('Post "%s" added.' % stored_entry.link)
              else:
                  msg.append('Post "%s" already saved.' % stored_entry.link)
          self.updated = utils.get_datetime_now()
          self.save(no_signals=True)
          return '<br />'.join(msg)
docs: This method should be called to update associated Posts
          It will call content-specific methods:
               _get_data() to obtain list of entries
               _store_post() to store obtained entry object
               _get_data_source_url() to get an URL to identify Posts from this Data Source