i am trying to run this data model code but error is all i get

Question

// front end code

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Student.aspx.cs" Inherits="nekmAdo.Student" %>

<title></title>

<form id="form1" runat="server">

    <div>

        <table>

            <tr>

                <td>Student_Id</td>

                <td>

                    <asp:TextBox Student_Id="txtStudent_Id"
                        runat="server"></asp:TextBox>

                </td>

            </tr>

            <tr>

                <td>Name</td>

                <td>

                    <asp:TextBox Name="txtName"

                        runat="server"></asp:TextBox>

                </td>

            </tr>

            <tr>

                <td>Email</td>

                <td>

                    <asp:TextBox Email="Email"
                        runat="server"></asp:TextBox>

                </td>

            </tr>

            <tr>

                <td>Join_Date</td>

                <td>

                    <asp:TextBox Join_Date="Join_Date"
                        runat="server"></asp:TextBox>

                </td>

            </tr>

            <tr>

                <td colspan="2">
                    <asp:Button ID="btnSubmit" runat="server"
                        Text="Submit" OnClick="btnSubmit_Click"/>

                </td>

            </tr>

            <tr>

                <td colspan="2">
                    <h5>Message: <asp:Label ID="lblMessage"
                        runat="server"></asp:Label></h5>


                </td>

            </tr>

        </table>


    </div>

</form>

// Back end 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.SqlClient;

namespace nkemAado

{

public partial class CreateStudent : System.Web.UI.Page

{

        Protected void btnSubmit_Click(object Sender, EventArgs e)

        {

        string connectionString = @"Data Source=DESKTOP-5JPBK1L; Database=StudentDB; 

Integration Security=SSPI";

            STUDENT_TABLE student_table = new STUDENT_TABLE()

            {

                STUDENT_ID = Convert.ToInt32(txtStudent_Id.Text),

                NAME = txtName.Text,

                EMAIL = txtEmail.Text,

                JOIN_DATE = DateTime.Parse(txtJoinDate.Text)

            };

        using (SqlConnection cn = new SqlConnection(connectionString))

        using (SqlCommand cmd = new SqlCommand(sql, cn))

        {

            cn.Open();

            cmd.ExecuteNonQuery();

            cn.Close();

        }

        try

            {

                using (StudentDBEntities StudentDB = new StudentDBEntities())

                {

                    StudentDB.STUDENT_TABLE.Add(student_table);

                    StudentDB.SaveChanges();

                }

                lblMessage.Text = "Student Created successfully!";

            }

            catch (Exception excp)

            {

                lblMessage.Text = "Error: " + excp.Message;

            }

        }

    
}

}