ASP.NET Web PDF Document Viewer/Editor Control Library

A common scenario where you may think of using scrollable result sets is when you want to paginate through a query s results. By paginate, I mean scrolling back and forth n rows out of a total number of m rows. For example, say n equals 10 and m equals 100. In this case, the first ten rows would be displayed to the user in the beginning. The user can navigate to the next ten rows by clicking a Next button (or its GUI equivalent). The user navigates to the previous ten rows by clicking a Previous button. At any given time, the user is looking at a window of ten rows out of a total of 100 rows. A typical requirement in this case is to also be able to sort the query results based on one or more of the columns. There are many approaches to solving this scenario. Use a scrollable result set and scroll back and forth n rows using one of the many positioning methods you learned about earlier. This approach has the following limitations: Since a ResultSet is associated with a Connection object, you have to hold the connection across requests in the case of web applications. This is feasible only in the case of client/server applications and is not a recommended practice for web applications, as discussed in the section Web Applications and ConnectionRelated Challenges of 14. For sorting on query columns, you will have to reissue the query.

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If you have previous experience working with Forms authentication under .NET 1.x, you will be happy to know that your existing code is 100 percent backwards compatible (as are most other aspects of ASP .NET 2.0). As you would suspect, ASP .NET 2.0 provides a number of new types to simplify Forms-based authentication. However, before examining these new items, let s review the core model. To leverage Forms-based authentication under ASP .NET, the first step is to author a custom aspx file that will provide the necessary UI to prompt for user credentials, such as a username and password. Figure 5-8 illustrates a typical logon.aspx page consisting of two TextBoxes, a handful of Labels and RequiredFieldValidators, and a Button type used to post back to the web server.

This would only work for small result sets, since caching a large result set can bring down your JVM due to excessive memory consumption This suffers from various limitations associated with scrollability, as discussed in the section Result Set Limitations Use a forward-only result set and cache all the rows in the middle tier Subsequent user interactions work on the cached rows This approach has the following limitations: You can sort your rows in the middle-tier cache, but you have to write extra code for that This gets more complicated if you want to sort multiple columns It has the drawback of excessive memory consumption in the middle tier in the case of large result sets Use a forward-only result set and issue a query each time the user navigates to a new window.

such as to access the array via an accessor function or object that performs one or more internal index adjustments before looking up the underlying array. If you add support for the slicing operators to your own types, you can choose whether they return copies of data structures or an accessor object.

Figure 5-8. Building a Logon.aspx page The Button s server-side Click event handler is responsible for extracting the supplied username and password values and validating them against the previously persisted values, which again may be located in a server-side XML file or, more commonly, in a table in a given database. Once you determine that the credentials are valid, the final step is to call the static FormsAuthentication.RedirectFromLoginPage method to attach the authentication cookie and redirect the user to the requested page. Consider the following logic: public class Logon : System.Web.UI.Page { protected void btnSubmit_Click(object sender, EventArgs e) { // Scrape out uid and pwd. string uid = txtUserName.Text; string pwd = txtPassword.Text; // Call a helper function to determine valid user. if (UserIsValid(uid, pwd)) // Success! Redirect user to requested page. FormsAuthentication.RedirectFromLoginPage(uid, false); else // Oops! User not found. Display error message.