6: Fetching and Presenting Data with SqlDataSource in .NET

Encode QR Code in .NET 6: Fetching and Presenting Data with SqlDataSource

Session variables die when the user closes the browser Even if the user leaves the browser open, the Session expires 20 minutes (the default) after the last page visit or refresh at the Web site To create a page that sets a Session variable, follow these steps: 1 Add a new ASPNET page called Sessionaspx to your project 2 From the Toolbox, add TextBox, Button, and HyperLink controls to the page 3 Select the HyperLink control and in its Properties window (F4), set the NavigateUrl property to starteraspx, the page you used previously to display the DetailsView 4 In Design view, double-click the Button control to create an event handler for the Click event The IDE switches to Source view (For more on event handlers, see 5) 5 In the event handler for the Click event, in the line above the End Sub statement, type the following line of code: Session( strCountry ) = TextBox1Text The preceding code fetches the value typed into TextBox1 and stores it in a Session variable on the Web server Now that you have a way of setting the Session variable, you need to configure starteraspx to read and use the stored value To configure the SqlDataSource to use a Session variable, do the following: 1 Open starteraspx (the page from previous examples that includes the DetailsView control) 2 Remove the DropDownList control (its ID is ddlCountries) by selecting the control and pressing the Delete key 3 Select the SqlDataSource control (The ID is likely SqlDataSource1 Don t use the one called SqlDSCountries) 4 Open the SqlDataSource control s Properties window (F4), select the SelectQuery property and, in the right-hand column, click the ellipsis button 5 In the Command and Parameter Editor, from the Parameter Source drop-down list, choose Session See Figure 6-11 6 In the Session Field box, type strCountry, as shown in Figure 6-11 7 Click OK

In this example, the sessionaspx page sets the Session variable and provides a way to navigate to the DetailsView page (starteraspx) where the SqlDataSource controls picks up the Session value and uses it as its parameter Here s how to test the pages: 1 Browse to sessionaspx 2 In the text box, type France and click the button Nothing much appears to happen, but behind the scenes, the button s event handler set the Session variable to France 3 Click the hyperlink to navigate to starteraspx, which contains the DetailsView control The page opens with the DetailsView control showing the first customer from France and navigation links to the remaining French customers Session variables are handy but too many can gobble up the Web server s memory and cause the server to misbehave

You ve certainly seen thousands of query string parameters even if you didn t know what they re called The following is a URL from a famous ASPNET Web site The query string starts at the question mark ( ) and continues to the end:

http://wwwkencoxca/Servicesaspx catId=c02 This query string includes a name/value pair The name in this case is catId and the value is c02 When the Web server sees a query string, it passes the information to ASPNET for further processing The SqlDataSource control can pick out the value and use it as part of a SQL query Follow these steps to create a query string that passes a value: 1 Open starteraspx, the ASPNET page that includes the DetailsView control 2 From the Toolbox, add an ASPNET HyperLink control to the page 3 In the HyperLink control s Properties window, insert the following value for the NavigateUrl property: ~/starteraspx country=UK When you click the hyperlink, the browser requests the current page (starteraspx) and at the same time passes the name/value pair country/UK Follow these steps to tell the SqlDataSource control to use the query string value when getting data: 1 Select the SqlDataSource control (the ID is likely SqlDataSource1 and not SqlDSCountries) 2 In the SqlDataSource control s Properties window (F4), select the SelectQuery property, and click the ellipsis button in the right-hand column 3 In the Command and Parameter Editor, choose QueryString from the Parameter Source drop-down list 4 In the QueryStringField box, type country and then click OK When you run the page and click the hyperlink, the SqlDataSource reads the value (UK) from the query string and uses it as part of the SQL query