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Because multiple users can visit the same web page concurrently, it is possible for a user visiting a data modification page to inadvertently overwrite the modifications made by another user. Consider a page with an editable GridView. If two users visit this page simultaneously from different computers and both edit the same row, whomever saves the first will have her changes overwritten by whomever saves the row last. This type of behavior is known as "last write wins" and is the default behavior for web applications..

Starting with ASP.NET 3.5 SP 1, the ScriptManager control in the ASP.NET AJAX Framework includes functionality for creating history points in an AJAX-enabled web page. Adding a history point creates an entry in the browser's history for a particular page state.

This article shows how to add history points using the ScriptManager control. In particular, it shows how to record history points whenever the user pages or sorts a GridView.

An enumeration is a special type in the .NET Framework that is comprised of a number of named constants. While you might not have created an enumeration type yourself, you have likely used enumerations many times in day-to-day programming. For example, the rows in a GridView have a RowType property that returns an enumeration of type DataControlRowType that indicates the row's type: Header, Footer, DataRow, and so on.

When working with an enumeration we may need to display a descriptive message based on the enumeration's value. For example, using ASP.NET's Membership system you can programmatically create a new user account calling the Membership class's CreateUser method. This method specifies the success or failure of the operation via the MembershipCreateStatus enumeration. This enumeration has members like Success, InvalidUserName, InvalidPassword, DuplicateUserName, and the like. When calling this method from an ASP.NET page you might want to show the user a descriptive message based on this enumeration value.

This article explores three different ways to provide descriptive text for enumeration members.

A common type of report is the master/detail report, in which the report begins by showing some set of "master" records. The user can then drill down into one of the master records, thereby viewing that master record's "details." Master/detail reports are an ideal choice for visualizing one-to-many relationships, such as a report showing all of the categories and then allowing a user to select a particular category and display its associated products. Additionally, master/detail reports are useful for displaying detailed information from particularly "wide" tables (ones that have a lot of columns). For example, the "master" level of a master/detail report might show just the product name and unit price of the products in the database, and drilling down into a particular product would show the additional product fields (category, supplier, quantity per unit, and so on).

There are many ways with which a master/detail report can be implemented. Over this and the next three tutorials we'll look at a variety of master/detail reports. In this tutorial we'll see how to display the master records in a DropDownList control and the details of the selected list item in a GridView. In particular, this tutorial's master/detail report will list category and product information.