private void UpdateInstructorCourses(string[] selectedCourses, Instructor instructorToUpdate)
        {
            if (selectedCourses == null)
            {
                instructorToUpdate.Courses = new List<Course>();
                return;
            }

            var selectedCoursesHS = new HashSet<string>(selectedCourses);
            var instructorCourses = new HashSet<int>
                (instructorToUpdate.Courses.Select(c => c.CourseID));
            foreach (var course in db.Courses)
            {
                if (selectedCoursesHS.Contains(course.CourseID.ToString()))
                {
                    if (!instructorCourses.Contains(course.CourseID))
                    {
                        instructorToUpdate.Courses.Add(course);
                    }
                }
                else
                {
                    if (instructorCourses.Contains(course.CourseID))
                    {
                        instructorToUpdate.Courses.Remove(course);
                    }
                }
            }
        }
 private void PopulateAssignedCourseData(Instructor instructor)
 {
     var allCourses = db.Courses;
     var instructorCourses = new HashSet<int>(instructor.Courses.Select(c => c.CourseID));
     var viewModel = new List<AssignedCourseData>();
     foreach (var course in allCourses)
     {
         viewModel.Add(new AssignedCourseData()
         {
             CourseID = course.CourseID,
             Title = course.Title,
             Assigned = instructorCourses.Contains(course.CourseID)
         });
     }
     ViewBag.Course = viewModel;
 }