Read data from dynamic ASP.Net Table inside GridView on Button click

HTML

<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
    runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:TemplateField HeaderText="Select">
            <ItemTemplate>
                <asp:CheckBox ID="chkSelect" OnCheckedChanged="SelectOrders" AutoPostBack="true"
                    runat="server" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="CustomerId" HeaderText="CustomerId" ItemStyle-Width="30" />
        <asp:BoundField DataField="ContactName" HeaderText="ContactName" ItemStyle-Width="150" />
        <asp:TemplateField HeaderText="Orders">
            <ItemTemplate>
                <asp:Table ID="tblOrders" runat="server">
                </asp:Table>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

VB.Net

Namespaces

Imports System.Data.SqlClient
Imports System.Data

VB Code

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.PopulateCustomers()
    End If

    PopulateOrders()
End Sub

Private Sub PopulateOrders()
    For Each row As GridViewRow In Me.GridView1.Rows
        Dim customerId As String = row.Cells(1).Text
        Dim table As Table = TryCast(row.FindControl("tblOrders"), Table)
        Dim constr As String = ConfigurationManager.ConnectionStrings("Constr").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand("SELECT TOP 5 OrderId FROM Orders WHERE CustomerId = @CustomerId", con)
                cmd.Parameters.AddWithValue("@CustomerId", customerId)
                con.Open()
                Dim sdr As SqlDataReader = cmd.ExecuteReader()
                While sdr.Read()
                    Dim tdRow As New TableRow()

                    For i As Integer = 0 To sdr.FieldCount - 1
                        Dim cell As New TableCell()
                        cell.Text = sdr.GetValue(i).ToString()
                        tdRow.Cells.Add(cell)
                    Next

                    table.Rows.Add(tdRow)
                End While
                con.Close()


            End Using
        End Using
    Next
End Sub

Protected Sub SelectOrders(sender As Object, e As EventArgs)

    If TryCast(sender, CheckBox).Checked Then

        Dim row As GridViewRow = TryCast(TryCast(sender, CheckBox).NamingContainer, GridViewRow)
        Dim table As Table = TryCast(row.FindControl("tblOrders"), Table)
        Dim message As String = String.Empty
        For Each tableRow As TableRow In table.Rows
            message += tableRow.Cells(0).Text + ","
        Next
        message = message.Substring(0, message.LastIndexOf(","))
        ClientScript.RegisterStartupScript(Me.[GetType](), "alert", (Convert.ToString("alert('") & message) + "')", True)
    End If
End Sub

Private Sub PopulateCustomers()
    Dim constr As String = ConfigurationManager.ConnectionStrings("Constr").ConnectionString
    Using con As New SqlConnection(constr)
        Using cmd As New SqlCommand("SELECT TOP 5 * FROM Customers", con)
            Using da As New SqlDataAdapter(cmd)
                Dim dt As New DataTable()
                da.Fill(dt)
                GridView1.DataSource = dt
                GridView1.DataBind()
            End Using
        End Using
    End Using
End Sub

C#.Net

Namespaces

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

 C#

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

    PopulateOrders();
}

private void PopulateOrders()
{
    foreach (GridViewRow row in this.GridView1.Rows)
    {
        string customerId = row.Cells[1].Text;
        Table table = row.FindControl("tblOrders") as Table;
        string constr = ConfigurationManager.ConnectionStrings["Constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT TOP 5 OrderId FROM Orders WHERE CustomerId = @CustomerId", con))
            {
                cmd.Parameters.AddWithValue("@CustomerId", customerId);
                con.Open();
                SqlDataReader sdr = cmd.ExecuteReader();
                while (sdr.Read())
                {
                    TableRow tdRow = new TableRow();

                    for (int i = 0; i < sdr.FieldCount; i++)
                    {
                        TableCell cell = new TableCell();
                        cell.Text = sdr.GetValue(i).ToString();
                        tdRow.Cells.Add(cell);
                    }

                    table.Rows.Add(tdRow);
                }
                con.Close();
            }


        }
    }
}

protected void SelectOrders(object sender, EventArgs e)
{
    if ((sender as CheckBox).Checked)
    {
        GridViewRow row = (sender as CheckBox).NamingContainer as GridViewRow;
        Table table = row.FindControl("tblOrders") as Table;
        string message = string.Empty;
        foreach (TableRow tableRow in table.Rows)
        {
            message += tableRow.Cells[0].Text + ",";
        }
        message = message.Substring(0, message.LastIndexOf(","));
        ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('" + message + "')", true);
    }
}

private void PopulateCustomers()
{
    string constr = ConfigurationManager.ConnectionStrings["Constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT TOP 5 * FROM Customers", con))
        {
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                DataTable dt = new DataTable();
                da.Fill(dt);
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }
        }
    }
}

Screenshot