public ActionResult AssignTeacher(CourseAssign courseAssign)
        {
            if (!ModelState.IsValid)
            {
                ViewBag.Departments = departmentBll.GetDepartments();
                return(View("AssignTeacher"));
            }

            ViewBag.Message     = courseBll.SaveAssignTeacher(courseAssign);
            ViewBag.Departments = departmentBll.GetDepartments();
            return(View());
        }