从主键asp.net获取SQL外键列值c＃

Question

我有两个表，一个是教师，另一个是调度。教师表具有主键TID和其他列。 Scheduling表具有主键，其他列和外键TID。

现在，我将教师数据插入一个页面。它成功插入。我必须在其他页面中插入数据，以便与学生一起安排教师的课程。我的问题是这个，我不能在调度表的fk列中插入教师的pk值。

这是我到目前为止所做的。

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

namespace E_Tutor_Manager
{
    public partial class ScheduleClass : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            {
                string connc = @"Data Source=KHAWAR-PC.\SQLEXPRESS;Initial Catalog=ETManager;Integrated Security=True";
                SqlConnection con = new SqlConnection(connc);
                string query = "SELECT Username FROM Teachers";
                SqlCommand cmd = new SqlCommand(query, con);
                cmd.Connection.Open();
                SqlDataReader ddlValues;
                ddlValues = cmd.ExecuteReader();
                TUName.DataSource = ddlValues;
                TUName.DataValueField = "Username";
                TUName.DataTextField = "Username";
                TUName.DataBind();
                cmd.Connection.Close();
                cmd.Connection.Dispose();
            }

            if (!IsPostBack)
            {
                if (Session["New"] != null)
                {
                    welcome.Text += Session["New"].ToString();
                }
                else
                    Response.Redirect("Login.aspx");
            }
        }

        protected void Button1_Schedule_Click(object sender, EventArgs e)
        {

            try
            {
                {
                    string connc = @"Data Source=KHAWAR-PC.\SQLEXPRESS;Initial Catalog=ETManager;Integrated Security=True";
                    SqlConnection con = new SqlConnection(connc);
                    con.Open();

                    string query = "SELECT * FROM Teachers WHERE StartTime = @StartTime";
                    string query1 = "INSERT INTO Schedules(Grade,Subjects,STime,TID) VALUES ('" + txtGrd.Text + "','" + Sbj.SelectedValue + "','" + txtTime.Value + "')";
                    SqlCommand sql = new SqlCommand(query1, con);
                    SqlCommand sql1 = new SqlCommand(query, con);
                    sql.ExecuteNonQuery();
                    var cmd = new SqlCommand(query, con);
                    cmd.Parameters.AddWithValue("@StartTime", txtTime.Value);
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    DataTable dt = new DataTable();
                    da.Fill(dt);
                    if (dt.Rows.Count > 0)
                    {
                        labelmsg.Text = "Sorry!!! This teacher is not available at this time. Please select the other teacher";
                    }
                    else
                    {
                        labelmsg.Text = "Class Scheduled Succesfully!!!";
                    }
                    con.Close();
                }        
            }
            catch (Exception ee)
            {
                throw (ee);
            }
        }

    }
}

那么有人可以帮助我吗？