class ItemStorage

class ItemStorage extends SqlContentEntityStorage implements ItemStorageInterface {
    
    /**
     * {@inheritdoc}
     */
    public function getItemCount(FeedInterface $feed) {
        $query = \Drupal::entityQuery('aggregator_item')->accessCheck(FALSE)
            ->condition('fid', $feed->id())
            ->count();
        return $query->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadAll($limit = NULL) {
        $query = \Drupal::entityQuery('aggregator_item');
        return $this->executeFeedItemQuery($query, $limit);
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadByFeed($fid, $limit = NULL) {
        $query = \Drupal::entityQuery('aggregator_item')->condition('fid', $fid);
        return $this->executeFeedItemQuery($query, $limit);
    }
    
    /**
     * Helper method to execute an item query.
     *
     * @param \Drupal\Core\Entity\Query\QueryInterface $query
     *   The query to execute.
     * @param int $limit
     *   (optional) The number of items to return.
     *
     * @return \Drupal\aggregator\ItemInterface[]
     *   An array of the feed items.
     */
    protected function executeFeedItemQuery(QueryInterface $query, $limit) {
        $query->accessCheck(FALSE)
            ->sort('timestamp', 'DESC')
            ->sort('iid', 'DESC');
        if (!empty($limit)) {
            $query->pager($limit);
        }
        return $this->loadMultiple($query->execute());
    }

}