/**
  * Returns the list of fields responsible to store attachment associations
  *
  * @return array [target_entity_class => field_name]
  */
 protected function getAttachmentTargets()
 {
     if (null === $this->attachmentTargets) {
         $this->attachmentTargets = $this->attachmentManager->getAttachmentTargets();
     }
     return $this->attachmentTargets;
 }