Calculate Total and Sub Total in Nested Child GridView in ASP.Net

Please refer this code:

HTML

<asp:GridView ID="gvOrders" runat="server" OnRowDataBound="gvOrders_RowDataBound"
    AutoGenerateColumns="false" HeaderStyle-BackColor="ActiveBorder" AlternatingRowStyle-BackColor="Bisque">
    <Columns>
        <asp:BoundField DataField="OrderId" HeaderText="OrderId" />
        <asp:TemplateField HeaderText="Product Name and Price">
            <ItemTemplate>
                <asp:GridView ID="Products" runat="server" ShowHeader="false" AlternatingRowStyle-BackColor="LightBlue"
                    GridLines="None" AutoGenerateColumns="false">
                    <Columns>
                        <asp:BoundField DataField="ProductName" ItemStyle-HorizontalAlign="Left" ItemStyle-Width="200" />
                        <asp:BoundField DataField="UnitPrice" ItemStyle-HorizontalAlign="Right" ItemStyle-Width="50" />
                    </Columns>
                </asp:GridView>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField HeaderText="Total" />
    </Columns>
</asp:GridView>

Namespaces

using System.Configuration;
using System.Data.SqlClient;
using System.Data;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.PopulateOrdersGrid();
    }
}

protected void gvOrders_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        string orderId = e.Row.Cells[0].Text;
        GridView gvProducts = e.Row.FindControl("Products") as GridView;
        this.PopulateProductsGrid(gvProducts, orderId);
        decimal total = 0;
        foreach (GridViewRow row in gvProducts.Rows)
        {
            total += Convert.ToDecimal(row.Cells[1].Text);
        }
        e.Row.Cells[2].Text = total.ToString();
    }
}

private void PopulateProductsGrid(GridView gv, string orderId)
{
    string constring = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constring))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT ProductName, products.UnitPrice  FROM Products products INNER JOIN [Order Details] OrderDetails ON OrderDetails.ProductId = products.ProductId " +
                                                    "WHERE OrderId = @OrderId"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Parameters.AddWithValue("@OrderId", orderId);
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                DataSet ds = new DataSet();
                sda.Fill(ds);
                gv.DataSource = ds;
                gv.DataBind();
            }
        }
    }
}

private void PopulateOrdersGrid()
{
    string constring = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constring))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT TOP 3 OrderId FROM Orders"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                DataSet ds = new DataSet();
                sda.Fill(ds);
                this.gvOrders.DataSource = ds;
                this.gvOrders.DataBind();
            }
        }
    }
}

SQL

I have used northwind database here.

Install the Northwind and Pubs Sample Databases in SQL Server Express

Screenshot