Apply Default Filter on Initial Load

You can set the initial filter for a RadGrid control so that when the Web page is first loaded, it presents an already-filtered set of data. To specify the initial filter,

• set the FilterExpression property of the MasterTableView (or detail GridTableView). The value of the FilterExpression property is a string that represents the text of a WHERE clause for filtering items. It operates in the same way as the DataView.Filter property.

• Set the CurrentFilterFunction and CurrentFilterValue properties of a column you want to use for filtering.

Setting the initial filter declaratively

The following example shows a grid that sets an initial filter so that when the Web page first appears, the only items that are displayed are from Germany:

<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" runat="server" AllowFilteringByColumn="True" AutoGenerateColumns="False"
DataSourceID="SqlDataSource1">
   <MasterTableView FilterExpression="([Country] LIKE '%Germany%')">
      <Columns>
        <telerik:GridBoundColumn CurrentFilterFunction="NoFilter" DataField="CustomerID"
            HeaderText="ID" UniqueName="CustomerID">
        </telerik:GridBoundColumn>
        <telerik:GridBoundColumn CurrentFilterFunction="NoFilter" DataField="CompanyName"
            HeaderText="Company" UniqueName="CompanyName">
        </telerik:GridBoundColumn>
        <telerik:GridBoundColumn CurrentFilterFunction="NoFilter" DataField="ContactName"
            HeaderText="Contact" UniqueName="ContactName">
        </telerik:GridBoundColumn>
        <telerik:GridBoundColumn CurrentFilterFunction="Contains" CurrentFilterValue="Germany"
            DataField="Country" HeaderText="Country" UniqueName="Country">
        </telerik:GridBoundColumn>
     </Columns>
   </MasterTableView>
</telerik:RadGrid>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
    SelectCommand="SELECT * FROM [Customers]" />

You can set the initial filter declaratively, as shown above, even when using the NeedDataSource event to populate the grid.

Setting the initial filter in the code-behind

You can use the grid's PreRender event to specify an initial filter. Note that after setting the filter, you must rebind the grid:

protected void RadGrid1_PreRender(object sender, System.EventArgs e)
{
    if (!Page.IsPostBack)
    {
        RadGrid1.MasterTableView.FilterExpression = "([Country] LIKE \'%Germany%\') ";
        GridColumn column = RadGrid1.MasterTableView.GetColumnSafe("Country");
        column.CurrentFilterFunction = GridKnownFunction.Contains;
        column.CurrentFilterValue = "Germany";
        RadGrid1.MasterTableView.Rebind();
    }
}

Protected Sub RadGrid1_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadGrid1.PreRender
    If (Not Page.IsPostBack) Then
        RadGrid1.MasterTableView.FilterExpression = "([Country] LIKE '%Germany%') "
        Dim column As GridColumn = RadGrid1.MasterTableView.GetColumnSafe("Country")
        column.CurrentFilterFunction = GridKnownFunction.Contains
        column.CurrentFilterValue = "Germany"
        RadGrid1.MasterTableView.Rebind()
    End If
End Sub

With the .NET 3.5 build of RadGrid for ASP.NET AJAX and LINQ filter expressions enabled (EnableLinqExpressions = true), the filter expressions set for the grid either internally by its filtering mechanism or manually in code should conform to the LINQ expression syntax instead of the old T-SQL syntax. Only thus they will be evaluated properly by the control.

If you are binding the grid using the NeedDataSource event, you can set the initial filter in the NeedDataSource event handler and omit the call to the Rebind method. The code for setting the filter must still be placed inside an if statement that checks that Page.IsPostBack is False . Note that this is applicable for non auto generated columns.

Setting FilterExpression for check box columns

When the grid contains a GridCheckBoxColumn, the syntax for the FilterExpression is slightly different, as shown in the following example:

<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" runat="server" AllowFilteringByColumn="True" AutoGenerateColumns="False"
  OnNeedDataSource="RadGrid1_NeedDataSource">
  <MasterTableView FilterExpression="([chkBoxColumnDataField] = True)">
    <Columns>
      <telerik:GridCheckBoxColumn UniqueName="BoolField" HeaderText="CheckBox Column" DataField="BoolField"
        AllowSorting="true" CurrentFilterFunction="EqualTo" CurrentFilterValue="True">
      </telerik:GridCheckBoxColumn>
    </Columns>
  </MasterTableView>
</telerik:RadGrid>