/**
  * Fetch a feed object given its feed URL.  If get a cache miss, fetch from the Datastore.
  * @param $feed_url URL of the feed.
  */
 public static function get($feed_url)
 {
     $mc = new Memcache();
     $key = self::getCacheKey($feed_url);
     $response = $mc->get($key);
     if ($response) {
         return [$response];
     }
     $query = parent::createQuery(self::FEED_MODEL_KIND);
     $feed_url_filter = parent::createStringFilter(self::SUBSCRIBER_URL_NAME, $feed_url);
     $filter = parent::createCompositeFilter([$feed_url_filter]);
     $query->setFilter($filter);
     $results = parent::executeQuery($query);
     $extracted = self::extractQueryResults($results);
     return $extracted;
 }