title: Clear cache when time is up in django
body: <p>I have problem with issue, with cache. I want to clear cache always when time is up.
  Below is part of my model in django 1.8 but app didn't used my method <code>clear_cache_when_times_up</code>.</p>
  
  <p>Is class model good place to clear cache when time is up?
  I want to  clear cache on list and on detail page, because there I use time.</p>
  
  <pre><code>class Article(BaseModel):
      title = models.CharField(max_length=255)
      short_text = models.TextField(max_length=10000, default='')
      livestream_url = models.URLField(default='', blank=True, null=True)
      livestream_from = models.DateTimeField('livestream from', blank=True, null=True)
      livestream_to = models.DateTimeField('livestream to', blank=True, null=True)
  
      def has_livestream(self):
          if self.livestream_from is None and self.livestream_to is None:
              return False
          return (self.livestream_from &lt;= timezone.now()) and (self.livestream_to &gt;= timezone.now())
  
      def clear_cache_when_times_up(self):
          if self.has_livestream():
              print('################## test #################')
              return cache.clear()
  </code></pre>