public ActionResult SaveReplacement(TeachersToReplaceViewModel model) { if (model == null) { return(RedirectToAction("Index")); } subjectService = new SubjectService(); teacherService = new TeacherService(); Teacher newTeacher = teacherService.GetTeacherById(model.Id); Subject subjectWithNewTeacher = hireTeacherSingleton.SubjectWhereTeacherWillBeReplaced; // assign new teacher to subject and save changes subjectService.ChangeSubjectTeacher(subjectWithNewTeacher, newTeacher); return(RedirectToAction("Index")); }