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Wrox WebShop

Figure 9-4

Design of the WebShop

To make the WebShop easy to maintain, it’s based on a three-tier architecture where the ASPX pages are separated from the business layer and data access code. The code for the business layer is located in the BusinessLogic folder in the special App_Code folder, and the data access layer can be found in the DataAccess folder. The presentation layer, consisting of .aspx and .ascx files, is located in the root of the site and in a few subfolders that are listed later.

The Business Layer

The business layer consists of five classes that are stored in the BusinessLogic folder inside the App_Code folder in the root of the web site.

Because each file in the business layer contains only one class, the file is named after the class. So you’ll find the Product class in the file Product.vb, and so on.

Product

The Product class (see Figure 9-5) represents the products that are displayed on the web site; it does not represent the actual ordered product customers can add to their shopping cart, although the two are closely related.

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Figure 9-5

The Product class itself has no defined behavior. That is, it has only properties and no methods other than a default constructor. All interaction with products, such as getting a list of products or a product instance, is carried out by the ShopManager class, which is discussed later. In addition to Id, Price, and Description properties, the Product class also has multiple PictureURL properties that are used to display images of the product in the product catalog, the detail page, and the shopping cart. The following table lists each of the eight properties of the Product class and explains their usage:

Property	Type	Description
CategoryId	Integer	The database of the WebShop has a Category table to
		identify the various product categories. Each product is
		then linked to that table through its CategoryId.
Description	String	This is the full description of the product, allowing you to
		provide detailed information about it.
Id	Integer	This is the unique ID of the product in the database. The
		ID is assigned by the database automatically whenever a
		new product is inserted.
PictureUrlLarge	String	This property contains a virtual path to the large image of
		the product. This image is used on the detail page for
		each product.
PictureUrlMedium	String	This property contains a virtual path to a medium-sized
		thumbnail image of the product. This image is used on
		the product catalog with a list of products.
PictureUrlSmall	String	This property contains a virtual path to a small thumbnail
		image of the product. This small image is used in the
		shopping cart.
Price	Decimal	The price of the product.
Title	String	This is the title of the product used to identify the prod-
		uct in the catalog and in the shopping cart.

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You should note that a product does not have properties like Quantity to indicate the number of items a user wants to order of a specific product. Whenever a user adds a product to the shopping cart, that product is wrapped inside an instance of the OrderedProduct class that does have these properties. The OrderedProduct class is discussed next.

OrderedProduct

In Figure 9-6, a diagram of the OrderedProduct class, you see a lot of properties that the Product class has as well. That’s no surprise, because an OrderedProduct has a lot in common with a Product. To avoid duplication of functionality and copying information from a Product to an OrderedProduct whenever an item is added to the shopping cart, the OrderedProduct class has a private member of type Product. When a new instance of an OrderedProduct is created, an instance of the Product class is passed to its constructor, which is then stored in _theProduct. Properties such as Description and PictureUrlSmall then forward their calls to the inner Product to get at the actual values.

Figure 9-6

Besides the properties that delegate their responsibility to the inner Product object, the OrderedProduct class has the following additional properties:

Property	Type	Description
Id	Guid	A unique ID to identify each product in the shopping cart.
		This ID is generated whenever a new instance of Ordered
		Product is created, and is used when existing items are
		updated or removed from the cart.
ProductId	Integer	The ID of the underlying product.
Quantity	Integer	The number of items of the product that a user has ordered.
SubTotal	Decimal	Returns the read-only subtotal for the OrderedProduct
		items by multiplying their quantity and the price of the
		inner Product. This property is used in the shopping cart
		to display the subtotal for each item.

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So far you have looked at classes that contain information, but cannot perform any actions. To do something useful with these classes you need some action classes that can operate on Products and OrderedProducts. Those classes are the ShoppingCart and the ShopManager, which are discussed next. Just as the Product and OrderedProduct classes, you’ll find these two classes in the BusinessLogic folder in the App_Code folder.

ShoppingCart

The ShoppingCart class (see Figure 9-7) is, as its name implies, the central storage location for OrderedProducts. An instance of the ShoppingCart class is stored in a simple session variable and made accessible through a shared property on the ShopManager class. This way, all the pages and other classes in the site can access the cart.

Figure 9-7

The ShoppingCart class contains a list with ordered products and a few methods to add, update, and remove those items. It also has properties to access the items in the shopping cart, get an item count, and get a total order amount for all the ordered products. Finally, it has a default, parameterless constructor to create new instances of type ShoppingCart.

The following table lists the properties of the ShoppingCart class:

Property	Type	Description
Count	Integer	Returns the total number of ordered items. It does
		this by looping through the _items collection,
		asking each OrderedProduct for its Quantity.
		This property is read-only.
Items	List (Of OrderedProduct)	Provides read-only access to the _items list. To
		add, update, or insert items in the list, the public
		methods of the ShoppingCart class must be used.
		This property is read-only.
Total	Decimal	Returns the total amount of money for the entire
		order. It does this by looping through the _items
		collection, asking each OrderedProduct for its
		SubTotal. This property is read-only.

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To work with the items in the shopping cart the class exposes the following methods:

Method Name	Return	Description
	Type
Public Sub Add	n/a	Adds a new OrderedProduct to the shopping
(ByVal theProduct		cart. When the item is already present, its quantity
As Product)		is increased instead of adding a new instance to the
		cart. The product passed to this method is wrapped
		inside an OrderedProduct instance that in turn is
		added to the cart.
Public Sub Clear ()	n/a	Removes all items from the cart.
Public Sub Remove	n/a	Removes an item from the cart based on its unique ID.
(ByVal id As Guid)
Public Sub Update	n/a	Updates the quantity for an existing item in the cart
(ByVal newQuantity		based on its unique ID.
As Integer, ByVal id
As Guid)

These four methods are never accessed by the ASPX pages in the presentation layer directly. The presentation layer should call one of the public methods on the ShopManager class that in turn call these methods on the ShoppingCart class.

ShopManager

The ShopManager class (see Figure 9-8) is the central entity in the application that deals with Products and OrderedProducts. It is used in two parts of the application: in the front end to provide access to the shopping cart and in the back end to allow an administrator to manage the products in the product catalog.

Figure 9-8

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In addition to the ShoppingCart property, which is of type ShoppingCart, discussed earlier, the ShopManager has the following public methods:

Method Name	Return	Description
	Type
Public Shared Sub	n/a	Adds a new OrderedProduct to the shopping
AddProductToCart		cart by calling the Add method of the Shopping
(ByVal theProduct		Cart class.
As Product)
Public Shared Sub	n/a	Deletes a product from the product catalog. This
DeleteProduct		method is used in the maintenance section of the
(ByVal theProduct		WebShop.
As Product)
Public Shared	Integer	Finalizes an order for a customer. This method
Function FinalizeOrder		calls the FinalizeOrder method in the data
(ByVal theCustomer		access layer to insert the order in the database
As Customer)		and then returns the new order ID.
Public Shared	Product	Returns a single instance of a product. This
Function GetProduct		method is used in the Product Details page to
(ByVal theProductId		display information about a specific product.
As Integer)
Public Shared	DataSet	Returns a DataSet with the available product
Function GetProduct		categories used in the catalog and the maintenance
Categories()		section.
Public Shared	List	Returns a list with products in the specified
Function GetProductList	(Of Product)	category. Used to display products in the product
(ByVal theCategoryId		catalog.
As Integer)
Public Shared Function	List	Returns a list with OrderedProducts from the
GetShoppingCartItems ()	(Of Ordered	ShoppingCart by accessing its Items property.
	Product)
Public Shared Sub	n/a	Inserts a new product in the product catalog. This
InsertProduct (ByVal		method is used in the maintenance section of the
theProduct As Product)		WebShop.
Public Shared Sub	n/a	Removes an OrderedProduct from the shopping
RemoveProductFromCart		cart by calling the Remove method of the Shopping
(ByVal id As Guid)		Cart class.
Public Shared Sub	n/a	Updates an existing OrderedProduct in the
UpdateProductInCart		shopping cart by calling the Update method of
(ByVal newQuantity		the ShoppingCart class.
As Integer, ByVal id
As Guid)

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Besides these methods, the ShopManager class has a single, hidden constructor. By hiding the constructor (using the access modifier Private) you can prevent calling code from creating useless instances of the ShopManager class. Because the class exposes only shared methods and properties, there is never the need for an instance of the ShopManager.

Obviously, a shop needs customers to stay in business and the Wrox WebShop is no exception. The next section shows you what the Customer class in the WebShop looks like.

Customer

The final class in the business layer you should look at is the Customer class. The WebShop uses the Membership provider and the Profile classes to store information about the user such as login name, password, and address details. Because all of this is handled by ASP.NET automatically, why do you need an additional Customer class?

The Customer class is used to reflect the user’s details at the moment of a purchase in the WebShop. From a security standpoint it’s a good practice to disallow users to change their details, such as the shipping address, after the purchase has been finalized. This way, for example, hackers cannot change the shipping address after the order has been paid and redirect the goods to their address instead of to the customer’s.

Right before the order is finalized in the Check Out page the Customer class is filled with the user’s details, which are retrieved from the Membership and Profile providers and then passed to the FinalizeOrder method in the ShopManager class. The details from the Customer class are inserted into the database together with the other order details. So, even if a customer changes the shipping address manually, the goods will still be delivered to the address that was supplied during the ordering process. If you want to allow customers to change their order details for an order that has already been finalized, you need to implement this functionality. To make this secure, you could allow them to temporarily update their details, but postpone applying the changes to the order until they have confirmed an e-mail, for example. This way, you can be sure that the original user has requested and approved the change.

The Customer class has only seven public properties and only one method, its constructor, as shown in Figure 9-9.

Figure 9-9

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Most of the properties are pretty straightforward and don’t need an additional explanation. The only exception is the CustomerId property. This ID, implemented as a Guid, is not generated by the Customer class itself, but is retrieved from the ProviderUserKey property of the MembershipUser class. This is the unique ID for each user in the application, automatically generated and stored by the ASP.NET Framework. Because the data stored by the Membership and Profile providers is in the same database used by the rest of the WebShop application, it makes sense to reuse this unique key so it’s easy to retrieve related user details later based on this key.

All properties of the Customer class are read-only — to set their initial values, you need to pass them to the constructor of the class.

Out of the five classes in the business layer, only the ShopManager has methods that require data access to read from and write to the database. This data access is performed by the ShopManagerDB class, which is discussed in the next section.

The Data Access Layer

Two key elements make up the data access layer. First there is the database and its tables that store the data for the shop. The second part contains the methods in the ShopManagerDB class that uses stored procedures to get data in and out of the database. Because a fundamental knowledge of the database is important to understand how the data access methods work, the data model is discussed first, followed by the ShopManagerDB class.

The Data Model

For many of the operations that take place in the WebShop, a back-end database is used. This database, called WebShop.mdf and stored in the App_Data folder of the web site, stores data about products, orders, and categories. To understand how it all fits together, you should take a look at Figure 9-10, which shows the data model for the WebShop. It’s quite a simple model, with only four tables.

Figure 9-10

Figure 9-10 shows only the custom tables added for the WebShop; it does not list the tables that have been added by the Membership and Role providers. During run time, those tables are used by the ASP.NET Framework to authenticate users and determine their roles. They are not used for storing information about products, categories, or orders, other than the CustomerId in the OrderBase table that is used to determine what WebShop user placed the order. The following tables list each database table and their respective columns:

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Product
	Column Name	Data Type	Description
	Id	int	The Unique ID of each product. This ID is generated
			automatically by the database each time a new product
			is inserted.
	Title	nvarchar(100)	The title of the product. The title is displayed on the
			product list and details pages of the product catalog.
	Description	nvarchar(max)	A longer description of the product. Although the
			nvarchar(max) data type, new in SQL Server 2005,
			allows you to store up to almost 2GB of information,
			the description is usually limited to a few K of text,
			describing the full product specs.
	Price	money	The price of the product.
	CategoryId	int	Each product is placed in a category that is displayed
			on the web site to allow for easy navigation of the
			product catalog. The names of the categories are stored
			in the Category table and the Product table stores only
			the primary key of that table as a foreign key.
	PictureUrlSmall	nvarchar(255)	A small picture showing the product. This image is
			shown in the shopping cart.
	PictureUrlMedium	nvarchar(255)	A medium-sized picture showing the product. This
			image is shown on the product list page.
	PictureUrlLarge	nvarchar(255)	A larger picture showing the product. This image is
			shown on the product details page.
	Deleted	bit	Indicates whether a product is still available on the
			web site. Because the product details are needed to
			display information about ordered products, a product
			can never be physically deleted from the database,
			Instead, it’s marked as “deleted.”

Each product is linked to a category that is stored in the Category table:

Category

Column Name	Data Type	Description
Id	int	The unique ID of each category. This ID is generated
		automatically by the database each time a new category
		is inserted.
Description	nvarchar(100)	The description of the category. The description of the
		category is used mainly in the navigation menu in the
		main shopping area to allow a user to select a category.

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Once a customer has placed an order, the order data is stored in two tables — OrderBase and OrderDetails. The OrderBase table contains information that applies to the entire order, such as the order date and the customer that placed the order.

OrderBase

Column Name	Data Type	Description
Id	int	The unique ID of each order. This ID is generated
		automatically by the database each time a new order
		is inserted. The order ID is also communicated back
		to the customer as the order number.
OrderDate	datetime	The date and time the order was placed.
CustomerId	uniqueidentifier	The ID of the customer that placed the order. This is
		the primary key of the aspnet_Users table that has
		been added to the database to support the Role and
		Membership providers.
FirstName	nvarchar(50)	The first name of the customer.
LastName	nvarchar(50)	The last name of the customer.
Street	nvarchar(100)	The customer’s shipping address.
ZipCode	nvarchar(20)	The zip code of the customer’s address.
City	nvarchar(100)	The city of the customer’s address.
Country	nvarchar(50)	The country of the customer’s address.

The OrderDetail table stores information about each product a customer has ordered. This table is linked back to the OrderBase table with its OrderBaseId column.

OrderDetail

Column Name	Data Type	Description
Id	int	The unique ID of each order detail record. This ID is
		generated automatically by the database each time a
		new order detail is inserted.
OrderBaseId	int	The ID of the order to which this order detail belongs.
ProductId	int	The ID of the ordered product. This ID is used to link
		back to the product table to get information such as
		the title and the description.
Price	money	Because a product’s price may change after it has been
		ordered, the price is stored with the order details. This
		ensures that the total price for an order doesn’t change
		after it has been confirmed by a customer.
Quantity	int	The number of items of the product the customer has
		ordered.

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