Single expand in hierarchical grid

In some particular scenarios you may want to allow single row expand at a time for each level in the grid hierarchy (due to user preference, custom development conventions, etc.). This feature is not built-in for Telerik RadGrid, however you can provide with only several lines of code. You merely need to:

1. Hook the ItemCommand event and check whether e.CommandName is RadGrid.ExpandCollapseCommandName

2. Traverse all items in the currently active GridTableView

3. Set the Expanded property for all items which differ from the e.Item instance to false

And here is the code of a simple demo:

<telerik:RadGrid RenderMode="Lightweight" ID="RadGrid1" runat="server" AutoGenerateColumns="False">
  <MasterTableView DataKeyNames="CustomerID" Width="100%">
    <DetailTables>
      <telerik:GridTableView DataKeyNames="OrderID" DataMember="Orders" Width="100%">
        <ParentTableRelation>
          <telerik:GridRelationFields DetailKeyField="CustomerID" MasterKeyField="CustomerID" />
        </ParentTableRelation>
        <DetailTables>
          <telerik:GridTableView DataKeyNames="OrderID" DataMember="OrderDetails">
            <ParentTableRelation>
              <telerik:GridRelationFields DetailKeyField="OrderID" MasterKeyField="OrderID" />
            </ParentTableRelation>
            <Columns>
              <telerik:GridBoundColumn SortExpression="UnitPrice" HeaderText="Unit Price" HeaderButtonType="TextButton"
                DataField="UnitPrice">
              </telerik:GridBoundColumn>
              <telerik:GridBoundColumn SortExpression="Quantity" HeaderText="Quantity" HeaderButtonType="TextButton"
                DataField="Quantity">
              </telerik:GridBoundColumn>
              <telerik:GridBoundColumn SortExpression="Discount" HeaderText="Discount" HeaderButtonType="TextButton"
                DataField="Discount">
              </telerik:GridBoundColumn>
            </Columns>
          </telerik:GridTableView>
        </DetailTables>
        <Columns>
          <telerik:GridBoundColumn SortExpression="OrderID" HeaderText="OrderID" HeaderButtonType="TextButton"
            DataField="OrderID">
          </telerik:GridBoundColumn>
          <telerik:GridBoundColumn SortExpression="OrderDate" HeaderText="Date Ordered" HeaderButtonType="TextButton"
            DataField="OrderDate">
          </telerik:GridBoundColumn>
          <telerik:GridBoundColumn SortExpression="EmployeeID" HeaderText="EmployeeID" HeaderButtonType="TextButton"
            DataField="EmployeeID">
          </telerik:GridBoundColumn>
        </Columns>
      </telerik:GridTableView>
    </DetailTables>
    <Columns>
      <telerik:GridBoundColumn SortExpression="CustomerID" HeaderText="CustomerID" HeaderButtonType="TextButton"
        DataField="CustomerID">
      </telerik:GridBoundColumn>
      <telerik:GridBoundColumn SortExpression="ContactName" HeaderText="Contact Name" HeaderButtonType="TextButton"
        DataField="ContactName">
      </telerik:GridBoundColumn>
      <telerik:GridBoundColumn SortExpression="CompanyName" HeaderText="Company" HeaderButtonType="TextButton"
        DataField="CompanyName">
      </telerik:GridBoundColumn>
    </Columns>
  </MasterTableView>
</telerik:RadGrid>

private void RadGrid1_NeedDataSource(object source, Telerik.Web.UI.GridNeedDataSourceEventArgs e)
{
    if (!e.IsFromDetailTable)
    {
        RadGrid1.DataSource = DataSourceHelperCS.GetDataTable("SELECT TOP 5 * FROM Customers");
    }

    RadGrid1.MasterTableView.DetailTables[0].DataSource = DataSourceHelperCS.GetDataTable("SELECT * FROM Orders");
    RadGrid1.MasterTableView.DetailTables[0].DetailTables[0].DataSource = DataSourceHelperCS.GetDataTable("SELECT * FROM [Order Details]");
}
private void RadGrid1_ItemCommand(object source, Telerik.Web.UI.GridCommandEventArgs e)
{
    if (e.CommandName == RadGrid.ExpandCollapseCommandName)
    {
        foreach (GridItem item in e.Item.OwnerTableView.Items)
        {
            if (item.Expanded && item != e.Item)
            {
                item.Expanded = false;
            }
        }
    }
}

Private Sub RadGrid1_NeedDataSource(ByVal [source] As Object, ByVal e As Telerik.Web.UI.GridNeedDataSourceEventArgs) Handles RadGrid1.NeedDataSource
    If Not e.IsFromDetailTable Then
        RadGrid1.DataSource = DataSourceHelperCS.GetDataTable("SELECT TOP 5 * FROM Customers")
    End If

    RadGrid1.MasterTableView.DetailTables(0).DataSource = DataSourceHelperCS.GetDataTable("SELECT * FROM Orders")
    RadGrid1.MasterTableView.DetailTables(0).DetailTables(0).DataSource = DataSourceHelperCS.GetDataTable("SELECT * FROM [Order Details]")
End Sub 'RadGrid1_NeedDataSource

Private Sub RadGrid1_ItemCommand(ByVal [source] As Object, ByVal e As Telerik.Web.UI.GridCommandEventArgs) Handles RadGrid1.ItemCommand
    If e.CommandName = RadGrid.ExpandCollapseCommandName Then
        Dim item As GridItem
        For Each item In e.Item.OwnerTableView.Items
            If item.Expanded AndAlso Not item Is e.Item Then
                item.Expanded = False
            End If
        Next item
    End If
End Sub