/**
  * @author sepo
  * @abstract
  * @return array all topics related to this newsletter
  */
 function getTopics()
 {
     if (empty($this->_topics) || !is_array($this->_topics)) {
         $this->_topics = array();
         if ($rs = executeQuery("SELECT * FROM topic WHERE newsletter_id='" . $this->getID() . "'")) {
             while ($row = $rs->getrow()) {
                 $topic = new cTopic();
                 $topic->set($row);
                 $this->_topics[] = $topic;
             }
         }
     }
     return $this->_topics;
 }