GridView中怎样删除数据库中的数据?急啊!

我按你们的提示改写的代码,在执行的时候提示是数据库的用户代码未处理 System.Data.SqlClient.SqlException
Message="DELETE 语句与 COLUMN REFERENCE 约束 'FK_Class_Teacher' 冲突。该冲突发生于数据库 'ST_DataBase'，表 'Class', column 'Class_teacher_id'。\r\n语句已终止。"请问在对表中有外键的时候怎么删除数据?
protected void Gv_teach_RowDeleting(object sender, GridViewDeleteEventArgs e)
{//删除数据
SqlConnection con = DB.CreateConn();
con.Open();
string sqlstr = "delete from Teacher where Teacher_id='"+Gv_teach.DataKeys[e.RowIndex].Value.ToString()+"'";
SqlCommand sqlcom = new SqlCommand(sqlstr, con);

sqlcom.ExecuteNonQuery();
try
{
sqlcom.ExecuteNonQuery();
Lbl_note.Text = "删除成功";

}
catch (SqlException)
{
Lbl_note.Text = "删除失败";
Lbl_note.Style["color"] = "red";
}
sqlcom.Connection.Close();
St_BindGridView();
}

给你一点参考代码：
//先绑定
private void bindTogvQz()
{
string strsql = ConfigurationManager.ConnectionStrings["qzsql"].ConnectionString;
SqlConnection con = new SqlConnection(strsql);
con.Open();
string selectstr = "select * from qztable";
SqlDataAdapter sda = new SqlDataAdapter();
sda.SelectCommand = new SqlCommand(selectstr,con);
DataSet ds = new DataSet();
sda.Fill(ds,"qzList");
string[] qz = new string[] {"qzID"};
this.gvQz.DataKeyNames = qz;
//this.gvQz.DataKeyNames = "qzID";
this.gvQz.DataSource = ds.Tables["qzList"].DefaultView;
this.gvQz.DataBind();
sda.Dispose();
con.Close();
con.Dispose();
}
//然后
protected void gvQz_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
//try
//{
string strID = this.gvQz.DataKeys[e.RowIndex].Value.ToString();
string strsql = ConfigurationManager.ConnectionStrings["qzsql"].ConnectionString;
SqlConnection con = new SqlConnection(strsql);
con.Open();
string deletestr = "delete from qztable where qzID=" + strID;
SqlCommand cmd = new SqlCommand(deletestr, con);
cmd.ExecuteNonQuery();
cmd.Dispose();
con.Close();
con.Dispose();
this.bindTogvQz();
//}
//catch
//{
// Response.Write("有点错误！");
//}
}

斑竹的意思是建立三层结构，将与数据库有关的代码全部写在数据访问层？偶现在在啃三层结构，数据访问层还容易理解，但业务逻辑层就一团晕……