public static function create_product($product)
 {
     if (strcmp($product['object_type'], self::PRODUCT) == 0) {
         $p = new Product();
     } else {
         if (strcmp($product['object_type'], self::SOLD_PRODUCT) == 0) {
             $p = new SoldProduct($product['number']);
         } else {
             if (strcmp($product['object_type'], self::IMPORT_PRODUCT) == 0) {
                 $p = new ImportProduct($product['import_price']);
             }
         }
     }
     //get data
     $p->get_data_from_array($product);
     return $p;
 }