public ActionResult AssignCourse(string Id, InstructorModels.AssignCourse model)
        {
            CourseInstructor assignment = new CourseInstructor();

            assignment.Course     = db.Courses.Single(c => c.Id == model.CourseId);
            assignment.AspNetUser = db.AspNetUsers.Single(c => c.Id == Id);
            db.CourseInstructors.Add(assignment);
            db.SaveChanges();
            return(RedirectToAction("ManageInstructors"));
        }
        public ActionResult AssignCourse(string Id)
        {
            InstructorModels.AssignCourse model = new InstructorModels.AssignCourse();
            List <Course> courses = db.Courses.ToList();

            foreach (CourseInstructor c in db.CourseInstructors)
            {
                courses.Remove(c.Course);
            }
            model.allCourses = courses;
            return(View(model));
        }