/**
  * @see DatabaseObjectList::readObjects()
  */
 public function readObjects()
 {
     parent::readObjects();
     // group by container id
     $groupedAttachments = array();
     foreach ($this->attachments as $attachment) {
         if (!isset($groupedAttachments[$attachment->containerID])) {
             $groupedAttachments[$attachment->containerID] = array();
         }
         $groupedAttachments[$attachment->containerID][$attachment->attachmentID] = $attachment;
     }
     $this->attachments = $groupedAttachments;
 }