AddToCart.aspx Page
Description: The AddToCart page adds the currently displayed product to
the user's shopping cart and then immediately redirects the browser to the
ShoppingCart.aspx page.
Implementation Notes: The AddToCart page is invoked when
users click the "Add to Cart" link in the product list page (ProductsList.aspx)
or in a product details page (ProductDetails.aspx).
The page displays no text. It simply gathers information, calls a process to
update the shopping cart, and then navigates to the shopping cart summary page
(ShoppingCart.aspx).
The ID of the product to add to the cart is passed to this page in the query
string. For example, if the user wants to add the "Mighty, Mighty Pen" to the
shopping cart, the URL to invoke this page would be
AddToCart.aspx?productID=371). Please review the referring pages to see how
this argument is added when constructing the hyperlink to this page.
The ProductsList page logic is encapsulated entirely within its Page_Load event
handler. This event handler is called when the page is accessed by a
browser client.
Page_Load Event Handler: The Page_Load event
handler obtains the specified ProductID parameter using the Params collection
of the page's Request object. The Params
collection contains all query string, form field, cookie, and server variables
sent from a client during an HTTP request. This the typical API through which
page developers access arguments when doing page to page navigation transfers.
The Page_Load event handler creates an instance of the ShoppingCartDB class and
calls its GetShoppingCartId method to get a "cart ID." The cart ID is created
either from the user's login name, or if the user has not yet logged in, from a
dynamically-generated GUID. If the cart ID is a GUID, the cart is a "temporary
shopping cart" that is good for the current session. This temporary cart is
automatically converted to a permanent cart when the user logs in and provides
their user name and password.
To actually add the item to the cart, the handler calls the AddItem method of
the ShoppingCartDB class, passing it the cart ID, the product ID, and the
quantity 1. Because the AddItem method expects an integer, the product ID,
which is a string when passed in the query string, is converted to an integer.
The AddItem method internally uses the ShoppingCartAddItem stored
procedure to update the shopping cart in the IBuySpy database.
Immediately after the item is added to the shopping cart, the user is
redirected to the ShoppingCart.aspx
page. The redirection is done using the Request object's Redirect method, which
causes a client-side redirect to the supplied URL. Causing this redirect to
occur immediately ensures that customers cannot accidentally re-add items to
the cart by clicking the Refresh button in the browser, because the URL will be
different after the redirect takes place.