Filtering Data with a DropDownList (but not by default)

pmarti · January 19th, 2014, 02:57 AM

Hi Imar,

I just finished building the pages that are created in Chapter 13. I'm using the DropDownList control to limit the number of records returned for the GridView. All is working as it should. I wanted to ask you if instead of setting the default selection in the DropDownList to "Make a Selection" with a null value, if it would be relatively easy to change the default selection to "All Genres" and have the default value be an expression that returns all records. It seems that this would be easier with a string in which you could use a wild card (*) as the default value, but in this case as probably many, the key value/field is an integer. Do you have any thoughts on how I could approach this variation?

Perhaps a slightly different approach in a situation where there are a large number of records, would be to have no records returned by default, but include a selection in the DropDownList (the last option in the list) that returns all genres. Can you think of how to incorporate such an option?

Your thoughts and approach would be greatly appreciated.
Thank you

Imar · January 19th, 2014, 08:24 AM

Hi there,

Yes, you can do that, like this:

1. First, set CancelSelectOnNullParameter on the SqlDataSource to False so it still executes the query even if the GenreId parameter is null.

2. Then update the SQL statement to it queries all records when the @GenreId parameter is null:

Code:

SelectCommand="SELECT [Id], [Title], [Authorized], [CreateDateTime] FROM [Review] WHERE ([GenreId] = @GenreId OR @GenreId IS NULL)"

This way, when there is no selected Genre, .NET will pass null for @GenreId, causing all records to be returned.

Hope this helps,

Imar

pmarti · January 19th, 2014, 01:31 PM

Imar,

That is exactly they type of solutions I was hoping for. Thank you very much for providing the information on how to change that behavior. Without the approach you provided I would have written a lot of code in the code beside page checking for the selected value of the DropDownList control. I can't tell you how much I appreciate all the help you've provided as I stumble through relearning web development.

Imar · January 19th, 2014, 02:40 PM

You're welcome....

Cheers,

Imar