protected function createAndPersistData()
 {
     foreach ($this->getReferences('product') as $product) {
         $productStock = new ProductStock();
         $productStock->setProduct($product)->setQuantity(rand(0, 1000));
         $warehouse = $this->getReference(sprintf('warehouse_%s', rand(1, 10)));
         $productStock->setWarehouse($warehouse);
         $this->manager->persist($productStock);
     }
 }