.NET Framework - DropDownList Binding to LINQ DataSource

Asked By JohnPadill

15-Dec-07 02:08 PM

I was playing around with the LINQtoSQL and found an interesting problem.

i am using the Northwind database on SQL 2005 Developer Server.
In my webform's PageLoad event I have the following code:

NorthwindDataContext db = new NorthwindDataContext();

var customers = from c in db.Customers
orderby c.CompanyName
select new
{
c.CompanyName,
c.CustomerID
};

ddCustomers.DataSource = customers;
ddCustomers.DataTextField = "CompanyName";
ddCustomers.DataValueField = "CustomerID";
ddCustomers.DataBind();

ddCustomers is a regular Asp.net DropDownList control.

The data populates correctly in the control at runtime.  The problem occurs
when i try to select an item in the list and the control's
SelectedIntexChanged event fires .

I need the CustomerID to populate a grid from another linq query but it
doesnt matter which item in the dropdownlist i choose, once the
selectedindexevent fires the index is always set to 0 and after the postback
finishes and the page is re-rendered the dropdownlist again shows the first
Customer inthe list (index = 0)

Note when I use the LinqDataSource control in replace of my page load query
and bind to the dropdownlist control it works perfectly normal.

21-Dec-07 02:13 AM

John-

Would it be beneficial to surround your data fetching code in Page_Load()
with:

if (!Page.IsPostback)
{

// code

}

Your code is refetching and rebinding your data each time--to the default
values.  Page_Load fires on each postback so, when your SelectedIndexChanged
fires and the page posts back, the data source resets. :)

HTH.

-dl

--
David R. Longnecker
http://blog.tiredstudent.com