public IActionResult ProductEdit(int id)
        {
            var model   = new ProductEditViewModel();
            var product = service.Product(id);

            if (product == null)
            {
                product = new Product
                {
                    CategoryID = service.Categories.FirstOrDefault().CategoryID,
                    SupplierID = service.Suppliers.FirstOrDefault().SupplierID,
                };
            }
            model.Category        = service.Categories.FirstOrDefault <Category>(c => c.CategoryID == product.CategoryID).CategoryName;
            model.Discontinued    = product.Discontinued;
            model.ProductID       = product.ProductID;
            model.ProductName     = product.ProductName;
            model.Supplier        = service.Suppliers.FirstOrDefault <Supplier>(s => s.SupplierID == product.SupplierID).CompanyName;
            model.QuantityPerUnit = product.QuantityPerUnit;
            model.UnitPrice       = product.UnitPrice;
            model.UnitsInStock    = product.UnitsInStock;
            model.UnitsOnOrder    = product.UnitsOnOrder;
            model.ReorderLevel    = product.ReorderLevel;

            model.suppliers  = service.Suppliers.Select(s => s.CompanyName);
            model.categories = service.Categories.Select(c => c.CategoryName);

            return(View(model));
        }
        public void Delete(int id)
        {
            var product = service.Product(id);

            if (product != null)
            {
                service.DeleteProduct(id);
            }
        }