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Session state is the heavyweight of state management. It allows information to be stored in one page and accessed in another, and it supports any type of object, including your own custom data types. Best of all, session state uses the same collection syntax as view state. The only difference is the name of the built-in page property, which is Session. Every client that accesses the application has a different session and a distinct collection of information. Session state is ideal for storing information such as the items in the current user s shopping basket when the user browses from one page to another. But session state doesn t come for free. Though it solves many of the problems associated with other forms of state management, it forces the web server to store additional information in memory. This extra memory requirement, even if it is small, can quickly grow to performance-destroying levels as hundreds or thousands of clients access the site.

Summary

You will encounter a few limitations when you bind directly to a DataReader. Because the DataReader is a forward-only cursor, you can t bind your data to multiple controls. You also won t have the ability to apply custom sorting and filtering criteria on the fly. Finally, unless you take care to code your page using generic interfaces such as IDataReader, you lock your code into the data provider you re currently using, making it more difficult to modify or adapt your code in the future. To solve these problems, you can use the disconnected ADO.NET data objects. If you fill a disconnected DataSet, you can bind that to one or more controls, and you can tailor the sorting and filtering criteria. The DataSet is also completely generic no matter which data provider you use to fill your DataSet, the DataSet itself (and the data binding code) looks the same. Technically, you never bind directly to a DataSet or DataTable object. Instead, you bind to a DataView object. A DataView represents a view of the data in a specific DataTable. That means the following: grid.DataSource = dataTable; grid.DataBind(); is equivalent to this: grid.DataSource = dataTable.DefaultView; grid.DataBind();

Session management is not part of the HTTP standard. As a result, ASP.NET needs to do some extra work to track session information and bind it to the appropriate response. ASP.NET tracks each session using a unique 120-bit identifier. ASP.NET uses a proprietary algorithm to generate this value, thereby guaranteeing (statistically speaking) that the number is unique and that it s random enough so a malicious user can t reverse-engineer or guess what session ID a given client will be using. This ID is the only piece of information that is transmitted between the web server and the client. When the client presents the session ID, ASP.NET looks up the corresponding session, retrieves the serialized data from the state server, converts it to live objects, and places these objects into a special collection so they can be accessed in code. This process takes place automatically.

In this chapter, you looked at data binding expressions and the ASP.NET data source controls in detail. Along the way, you started using the GridView, ASP .NET s premier rich data control. In the next chapter, you ll explore the three most powerful data-bound controls in detail: the GridView, DetailsView, and FormView. You ll also learn how they work with a few data source features that this chapter didn t cover, such as sorting and filtering.

It s important to note that every DataTable includes a default DataView object that s provided through the DataTable.DefaultView property. This sleight of hand allows you bind directly to the DataTable. If you do, ASP.NET actually uses the default DataView automatically. The default DataView doesn t apply any sort order and doesn t filter out any rows. If you want to tweak these settings, you can either configure the default DataView or create your own and explicitly bind it.

Earlier, you saw an example that allowed users to browse a list of cities in different regions using two linked controls a DropDownList and a GridView. Best of all, this example could be created using a SqlDataSource or an ObjectDataSource; either way, it doesn t require any custom code. Figure 9-9 shows this example. As convenient as this example is, it presents a problem that s difficult to fix. Because it s impossible to create a drop-down list that doesn t have a selected item (unless it s empty), the first city in the list is automatically selected. Many web applications use a different behavior and add an extra item at the top of the list with text such as (Choose a City) . Selecting this first item has no effect. Additionally, you might want to add an item that allows you to see every city in a single list. Figure 9-13 shows the result you want.