/**
  * singleton pattern
  *
  * @return PlentyItemDataPushWarehouse
  */
 public static function getInstance()
 {
     if (!isset(self::$instance) || !self::$instance instanceof PlentyItemDataPushWarehouse) {
         self::$instance = new PlentyItemDataPushWarehouse();
     }
     return self::$instance;
 }
 public function __construct()
 {
     /*
      * select some data, we will use them for new items
      */
     PlentyItemDataPushCategory::getInstance()->execute();
     PlentyItemDataPushWarehouse::getInstance()->execute();
     PlentyItemDataPushProducer::getInstance()->execute();
     $this->warehouseId = PlentyItemDataPushWarehouse::getInstance()->getFirstWarehouseId();
 }