How to extract extra data from LinqDataSource? - asp.net

Question

I have a simple wizard generated query in a LinqDataSource like this:
<asp:LinqDataSource ID="EvaluationsData" runat="server" ContextTypeName="Bonus.Models.BonusDataContext"
Select="new (Id, Name, Coverage)" TableName="BM_Evaluations"
</asp:LinqDataSource>
I assign this data source to a DropDownList, using Id and Name as the DataValueField and DataTextField respectively. But when I selected a option, I want to keep the Coverage too, extracting it from the data source and storage in a HiddenField. It's a way to do this without making another query to the database?
Thanks.

Answer 1

To do this, you'll need to intercept the returned list of items from the data source and then manually assign Coverage to the items in the drop-down's items.
Here's your markup
<asp:LinqDataSource ID="EvaluationsData" runat="server"
ContextTypeName="Bonus.Models.BonusDataContext"
Select="new (Id, Name, Coverage)" TableName="BM_Evaluations"
onselected="EvaluationsData_Selected">
</asp:LinqDataSource>
<asp:DropDownList ID="DropDownList1" runat="server"
DataSourceID="EvaluationsData" DataValueField="Id" DataTextField="Name"
ondatabound="DropDownList1_DataBound">
</asp:DropDownList>
Here's your code
List<object> evaluations;
protected void EvaluationsData_Selected(object sender, LinqDataSourceStatusEventArgs e)
{
evaluations = new List<object>(e.Result as IEnumerable<object>);
}
protected void DropDownList1_DataBound(object sender, EventArgs e)
{
foreach (ListItem item in DropDownList1.Items)
{
var eval = evaluations.Where(a => a.Id == item.Value).FirstOrDefault();
if (eval != null)
{
item.Attributes.Add("Coverage", eval.Coverage);
}
}
}