Inheritance: extends Pimcore\Model\Listing\JsonListing
 public function getPredefinedMetadataAction()
 {
     $type = $this->getParam("type");
     $subType = $this->getParam("subType");
     $list = Metadata\Predefined\Listing::getByTargetType($type, array($subType));
     $result = array();
     foreach ($list as $item) {
         /** @var $item Metadata\Predefined */
         $item->expand();
         $result[] = $item;
     }
     $this->_helper->json(array("data" => $result, "success" => true));
 }