public function getManufacturerByCategoryID()
 {
     if (!isset($_GET['id_category']) || !is_numeric($_GET['id_category'])) {
         return false;
     }
     $categories = new Product();
     $res = $categories->getManufacturerByCategoryID($_GET['id_category']);
     while ($row = PDOQuery::getInstance()->next_row($res)) {
         //$category_list .= '<li class="manufacturer-list"><a href="product_sale.php?id_manufacturer='.$row['id_manufacturer'].'">'.$row['manufacturer'].'</a></li>';
         $category_list .= '{"id_manufacturer": "' . $row['id_manufacturer'] . '", "manufacturer": "' . $row['manufacturer'] . '"},';
     }
     $category_list = '{"success": [' . rtrim($category_list, ',') . ']}';
     echo $category_list;
 }