public IActionResult OnPost(IFormFile imgProductUp, List <int> selectedShop)
      {
          if (!ModelState.IsValid)
          {
              return(Page());
          }
          int productId = _productService.AddProduct(Product, imgProductUp);

          _shopService.AddShopsToProduct(selectedShop, productId);
          return(RedirectToPage("Index"));
      }