private void UpdateDGV()
{
dbEntities db1 = new dbEntities();
db = db1;
List <Students_Tbl> lst = (from s in db.Students_Tbl select s).ToList();
stu_tbl.ItemsSource = lst;
stu_tbl.Columns[0].Visibility = Visibility.Hidden;
/* פעולה לעדכון הטבלה*/
}