<asp:GridView ID="grdViewCustomers" runat="server" AutoGenerateColumns="false" DataKeyNames="id_detailset" OnRowDataBound="grdViewCustomers_OnRowDataBound" CssClass="Grid">
	<Columns>
		<asp:TemplateField ItemStyle-Width="20px">
			<ItemTemplate>
				<a href="JavaScript:divexpandcollapse ('div<%# Eval("id_detailset") %>');"><img alt="Details" id="imgdiv<%# Eval("id_detailset") %>" src="images/plus.png" /></a>
				<!-- Adding the Div container -->
				<div id="div<%# Eval("id_detailset") %>" style="display: block;"><%--block вкл. для тестирования--%>
					<!-- Adding Child GridView -->
					<asp:GridView ID="GridView_child" runat="server" AutoGenerateColumns="false" DataKeyNames="id_detailset" CssClass="ChildGrid">
						<Columns>
							<asp:BoundField ItemStyle-Width="150px" DataField="id_directory" HeaderText="id_directory" />
							<asp:BoundField ItemStyle-Width="150px" DataField="name_directory" HeaderText="name_directory" />
						</Columns>
					</asp:GridView>
				</div>
			</ItemTemplate>
		</asp:TemplateField>
		<asp:BoundField ItemStyle-Width="150px" DataField="id_detailset" HeaderText="id_detailset" />
		<asp:BoundField ItemStyle-Width="150px" DataField="name_detailset" HeaderText="name_detailset" />
	</Columns>
</asp:GridView>

<asp:GridView ID="GridView_child" runat="server" AutoGenerateColumns="false" DataKeyNames="id_detailset" CssClass="ChildGrid">

        Dim GridView_child = CType(e.Row.FindControl("GridView_child"), GridView)
        'Dim GridView_child = DirectCast(e.Row.FindControl("GridView_child"), GridView)
        GridView_child.DataSource = SqlDataSource2
        GridView_child.DataBind()

GridView_child | Nothing

Protected Sub GridView_Parent_OnRowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
        Dim SqlDataSource2 As New SqlDataSource
        SqlDataSource2.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings("OrdersConnectSQL").ConnectionString

   If e.Row.RowType = DataControlRowType.DataRow Then
            SqlDataSource2.SelectCommand = "select * " & _
                                           "from name_table " & _
                                            "where column_name ='" & GridView_Parent.DataKeys(e.Row.RowIndex).Value.ToString() & "'"
        Dim GridView_child = CType(e.Row.FindControl("GridView_child"), GridView)
        GridView_child.DataSource = SqlDataSource2
        GridView_child.DataBind()
  end if
end sub