Saving and Retrieving Data with AJAX - Getting Data from a Database
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To see how to interact with a database, you’ll begin by creating a web application that can be used to display information about the AdventureWorks database. You’ll start out by simply retrieving and displaying a subset of data. These exercises will teach you how to connect your controls to a database to retrieve, filter, and sort the data and then use the myriad options for presenting it attractively.
As you may remember, AdventureWorks is a free database from Microsoft that represents a fictional company that sells outdoor and extreme sports gear. The database tracks products, inventory, customers, transactions, and suppliers.
See Chapter 1 for instructions on installing this sample database if you have not already done so.
ASP.NET includes a number of controls specifically designed for displaying data. We’ll focus on the GridView control, but other data controls include the DataList, Repeater, DetailsView, and FormView.
The GridView control displays columns and rows of data and allows sorting and paging. It is by far the most popular data display control and is ideal for understanding how data display controls interact with data-retrieval controls and code. The GridView control allows the user to click on a column header to sort the data. GridViews also let you present just a small subset of the data at one time, called a page, with links for easy access to other pages—this process is called “paging” through data. You can do these, and for numerous other data manipulations, with very little programming. A GridView with data from the AdventureWorks database is shown in Figure 4-1.
Binding Data Controls Database information is stored in memory as tables (just as it is retrieved from a relational database). Tables consist of rows and columns that match nicely to the GridView control.
You could write code to pick out each piece of data you want and write it into the appropriate row or column of the data control, but that’s time-consuming and error-prone. It is more efficient and safer to bind the control directly to the underlying data.
In the early days of Graphical User Interface (GUI) programming, binding was a bit of a “trick”—great for simple programs, but useless for commercial applications because the minute you wanted to do anything out of the ordinary, the binding would become a straitjacket. Microsoft has solved that with ASP.NET by exposing events on the Data Control that allow you to insert custom code at every stage of the retrieval and binding of the data to the control.
Figure 4-1. This GridView control displays data from the AdventureWorks database in a table format that makes it easier to read, and allows users to click the column headings to sort the data.
Binding is most often used with the larger data controls such as GridView, but you can also bind many other controls, such as DropDownList, ListBox, CheckBoxList, and RadioButtonList. All of these controls have a DataSource property that identifies the source to which the control is bound. For example, you might keep a list of all your customers’ names in a database. Binding that data to a ListBox can be a convenient way to allow a customer service representative to quickly pick a customer rather than typing in a name that might otherwise be difficult to spell.
To see how all this works, you’ll build the GridView from Figure 4-1. Once you have it up and running, you’ll add some features to it, including the ability to use the grid to update the database with new data!
Next: Create a Sample Web Page >>
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 This article is excerpted from chapter four of Learning ASP.NET 2.0 with AJAX: A Practical Hands-on Guide, written by Jesse Liberty, Dan Hurwitz and Brian MacDonald (O'Reilly, 2007; ISBN: 0596513976). Check it out today at your favorite bookstore. Buy this book now.
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