classic asp.net shoppingcart session state

Question

I have used this example to create a shopping cart : http://net.tutsplus.com/tutorials/other/build-a-shopping-cart-in-aspnet/

Its a good example, it stores the shoppingcart in the Session["cart"] state and it should all work fine.

BUT it doesn't. Event if close the browser, or try different browsers, it still maintains state?!?!

Here is the constructor + the add to cart method:

public List<CartItem> Items { get; private set; }

        // Readonly properties can only be set in initialization or in a constructor
        public static readonly ShoppingCart Instance;
        // The static constructor is called as soon as the class is loaded into memory
        static ShoppingCart()
        {
            // If the cart is not in the session, create one and put it there
            // Otherwise, get it from the session
            if (HttpContext.Current.Session["MPBooksCart"] == null)
            {
                Instance = new ShoppingCart();
                Instance.Items = new List<CartItem>();
                HttpContext.Current.Session["MPBooksCart"] = Instance;
            }
            else
            {
                Instance = (ShoppingCart)HttpContext.Current.Session["MPBooksCart"];
            }
        }
        // A protected constructor ensures that an object can't be created from outside
        protected ShoppingCart() { }

        public void AddItem(int book_id)
        {
            // Create a new item to add to the cart
            CartItem newItem = new CartItem(book_id);
            // If this item already exists in our list of items, increase the quantity
            // Otherwise, add the new item to the list
            if (this.Items.Contains(newItem))
            {
                foreach (CartItem i in Items)
                {
                    if (i.Equals(newItem))
                    {
                        i.Quantity++;
                        return;
                    }
                }
            }
            else
            {
                newItem.Quantity = 1;
                Items.Add(newItem);
            }

        }

May you please advise on what the issue might be?

I've read for about 2 hours regarding session state and everywhere it says it should be volatile when closing broser, but in this case it isn't.

Regards, Alex

Answer 1

I am not so sure about using a Singleton pattern to hold an instance of a session. If you think about it the session will need to be unique for each user and each browser that accesses the website. The Singleton pattern creates a single global unique instance. I don't know how much asp.net you have done but, just in case you are fairly new to asp.net a session will be unique to a specific browser instance. That means that each browser accessing the Session["MPBooksCart"] will access their own unique copy of the data. By default an asp.net session will hold its data for 20 minutes (this can be configured in the database). If I was writing a shopping cart I would probrably just work directly with a cart table and cartitems table in a database. A very good example of a storefront website is Rob Connery's MVC Samples App. This is an ASP.Net MVC application so if you aren't familiar with MVC you may find this a little bit hard to follow.