RadGrid (or LinqDataSource) querying whole table with allowpaging

[Sem]

(Working in VS 2010, C# 4.0, RadControls for ASP.NET AJAX 2010.2.929.40, Sql Server 2008)
When I have the following radgrid :

<telerik:RadGrid ID="RadGrid1" runat="server" AllowFilteringByColumn="True" AllowPaging="True"
        AllowSorting="True" GridLines="None" OnNeedDataSource="RadGrid1_NeedDataSource"
        AutoGenerateColumns="true" AutoGenerateEditColumn="true">
</telerik:RadGrid>

and this in my code behind :

protected void RadGrid1_NeedDataSource(object sender, GridNeedDataSourceEventArgs e)
{
    LinqDataSource ds = new LinqDataSource();
    ds.Selecting += (sd, evt) => evt.Result = new UserManager().GetAllUsers();
    RadGrid1.DataSource = ds;
}

3 queries are generated :

SELECT COUNT(*) AS [value]
FROM [dbo].[Portal_Users] AS [t0]

SELECT [t1].[Id], [t1].[FirstName], [t1].[LastName], [t1].[Email], [t1].[LastLogin], [t1].[Created]
FROM (
    SELECT ROW_NUMBER() OVER (ORDER BY [t0].[Id], [t0].[FirstName], [t0].[LastName], [t0].[Email], [t0].[LastLogin], [t0].[Created]) AS [ROW_NUMBER], [t0].[Id], [t0].[FirstName], [t0].[LastName], [t0].[Email], [t0].[LastLogin], [t0].[Created]
    FROM [dbo].[Portal_Users] AS [t0]
    ) AS [t1]
WHERE [t1].[ROW_NUMBER] BETWEEN @p0 + 1 AND @p0 + @p1
ORDER BY [t1].[ROW_NUMBER]

SELECT [t0].[Id], [t0].[FirstName], [t0].[LastName], [t0].[Email], [t0].[LastLogin], [t0].[Created]
FROM [dbo].[Portal_Users] AS [t0]

The first 2 queries are as expected but the 3rd one queries the whole users table. As this gives horrible performance with a large dataset I started digging around. Then I discovered that this :

<telerik:RadGrid ID="RadGrid1" runat="server" AllowFilteringByColumn="True" AllowPaging="True"
    AllowSorting="True" GridLines="None" DataSourceID="linqDS"
    AutoGenerateColumns="true" AutoGenerateEditColumn="true">
</telerik:RadGrid>
<asp:LinqDataSource ID="linqDS" OnSelecting="selecting" runat="server" />

and this in my codebehind :

protected void selecting(object sender, LinqDataSourceSelectEventArgs e)
{
    e.Result = new UserManager().GetAllUsers();
}

only gives the first 2 queries of the aforementioned 3 which solves my problem.

However, I don't know why in the first case I get 3 queries instead of 2. I would expect only the 2 queries in both cases. More worrying, I can imagine forgetting (me or my colleagues) that I must declare the LinqDataSource in the aspx page and not in my codebehind and so end up querying the whole table.

[Veli]

Hello Sem,

This is because when using the DataSourceID RadGrid knows it is binding to a data source control and applies a different set of databinding actions to benefit from the capabilities the data source control offers. This is not the case when setting the DataSource property of the control to the data source control instance. In any case, when using DataSource controls, the recommended approach is to pass them to the grid through the DataSourceID.

Veli
the Telerik team