insert data from asp.net page to my database with tables which have foreign key

Question

I'm a beginner asp.net programmer and my project is online shopping classes I have some problem in it

I have 4 tables with some foreign key between them...

CREATE TABLE [dbo].[orderdetails] 
(
    [orderid] INT NOT NULL,
    [classid] INT NOT NULL,

   CONSTRAINT [PK_orderdetails] 
      PRIMARY KEY CLUSTERED ([orderid] ASC, [classid] ASC)
);

CREATE TABLE [dbo].[order] 
(
    [orderid]    INT IDENTITY (300, 1) NOT NULL,
    [customerid] INT NOT NULL,

    CONSTRAINT [PK_order] 
       PRIMARY KEY CLUSTERED ([orderid] ASC)
);

CREATE TABLE [dbo].[customer] 
(
    [customerid] INT IDENTITY (200, 1) NOT NULL,
    [firstname]  NVARCHAR (50) NOT NULL,
    [lastname]   NVARCHAR (50) NOT NULL,
    [phone]      INT           NOT NULL,

    CONSTRAINT [PK_Table_1] 
       PRIMARY KEY CLUSTERED ([customerid] ASC)
);

CREATE TABLE [dbo].[class] 
(
    [classid]    INT IDENTITY (100, 1) NOT NULL,
    [numofclass] INT NOT NULL,
    [numofstud]  INT NOT NULL,
    [totalprice] INT NOT NULL,

    CONSTRAINT [PK_class] 
       PRIMARY KEY CLUSTERED ([classid] ASC)
);

FK_orderdetails_order
FK_order_customer
FK_orderdetails_class

I have three pages and in first page I pass some data to another page and in second page I set my data to my DB.

First page code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;  

public partial class _Default : System.Web.UI.Page
{
       static int totalprice = 0;

       protected void Page_Load(object sender, EventArgs e)
       {
           int studprice = Convert.ToInt32(Numofstud.SelectedValue) * 6;
           int classprice = Convert.ToInt32(Numofclass.SelectedValue) * 190;

           totalprice = studprice + classprice;
           lblTotalprice.Text = string.Format("{0}", totalprice);
       }

       protected void Numofstud_SelectedIndexChanged(object sender, EventArgs e)
       {
           int studprice = Convert.ToInt32(Numofstud.SelectedValue) * 6;
           int classprice = Convert.ToInt32(Numofclass.SelectedValue) * 190;

           totalprice = studprice + classprice;
           lblTotalprice.Text = string.Format("{0}", totalprice);
       }

       protected void Numofclass_SelectedIndexChanged(object sender, EventArgs e)
       {
                int studprice = Convert.ToInt32(Numofstud.SelectedValue) * 6;
                int classprice = Convert.ToInt32(Numofclass.SelectedValue) * 190;

                totalprice = studprice + classprice;
                lblTotalprice.Text = string.Format("{0}", totalprice);
            }

            protected void Registerbtn_Click(object sender, EventArgs e)
            {
                Session["Numofclass"] = Numofclass.SelectedItem.Value;
                Session["totalprice"] = totalprice;
                Session["Numofstud"] = Numofstud.SelectedItem.Value;

                Response.Redirect("account.aspx");
            }  
        }

Second page code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;  


public partial class account : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void buybtn_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["miztahrirtest2DB"].ToString());

        SqlCommand cmd = new SqlCommand("insert into customer (firstname, lastname, phone) values (@firstname, @lastname, @phone)", con);
        cmd.Parameters.AddWithValue("firstname", firstnametxt.Text);
        cmd.Parameters.AddWithValue("lastname", lastnametxt.Text);
        cmd.Parameters.AddWithValue("phone", phonetxt.Text);

        con.Open();
        cmd.ExecuteNonQuery();
        con.Close();

        SqlCommand cmd2 = new SqlCommand("insert into class (numofstud, numofclass, totalprice) values (@numofstud, @numofclass, @totalprice)", con);
        cmd2.Parameters.AddWithValue("numofclass", Session["Numofclass"]);
        cmd2.Parameters.AddWithValue("numofstud", Session["Numofstud"]);
        cmd2.Parameters.AddWithValue("totalprice", Session["totalprice"]);

        con.Open();
        cmd2.ExecuteNonQuery();
        con.Close();

        SqlCommand cmd3 = new SqlCommand("insert into order ....

        Response.Redirect("bank.aspx");
    }
}

My problem is that I don't know how to insert value into tables which have foreign key and primary key.cmd1 and cmd2 are working correctly but I can't write something to set order table and orderdetails table which They have a foreign key from another table...

Answer 1

When you inserting parent table you should put scope_identity() end of insert command. And you should use execute scalar. Scope identity give you inserted id by execute scalar. After then you can insert child items with this parent id.