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Database SQL ServerAccessing and Updating Data in ASP.NET 2.0: Handling Database NULL Values
Author: aspnet.4guysfromrolla.com |
Published: 28th Nov 2007 |
Visited: 78 times |
Add CommentFiled in: SQL Server
In the last two installments of this article series -
Updating Basics and Customizing the
Editing Interface - we saw how to configure the SqlDataSource control to issue UPDATE statements to a
database and how to then configure the GridView control to work in tandem with the SqlDataSource control to provide a
web-based editing interface. By default, the GridView's editing interface renders a TextBox for each editable column in the
grid. However, in certain scenarios we may want to customize the editing interface by including validation controls or by
using an alternative Web control to collect the user's input. In particular, we customized the editing interface so that
when editing a product from the Northwind database, a user could select the product's category through a DropDownList
control rather than having to enter the actual CategoryID value into a TextBox.
While the Customizing the Editing Interface article provided a complete, working example of creating a customized
editing interface, it had one potentially criticial shortcoming - the approach did not work with products that had a
NULL database value for their CategoryID. For starters, the SELECT query used to
populate the GridView used an INNER JOIN, which only returned those products with a matching category record.
But even if we update the query to use a LEFT JOIN, the DropDownList in the customized editing interface did
not include a list item representing the NULL value, so a user would be unable to edit a product and change
the category from an existing value to NULL.
In this article we will look at how to customize the DropDownList in the editing interface such that it can correctly
handle database NULL values. Read on to learn more!
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