public IActionResult Get(int studentId, int courseId) { var student = studentRepository.GetById(studentId); if (student == null) { return(NotFound("Student does not exist.")); } var course = courseRepository.GetById(courseId); if (course == null) { return(NotFound("Course does not exist.")); } var mark = marksRepository.GetMarksModel(studentId, courseId); if (mark == null) { return(NotFound("Mark does not exist.")); } return(Ok(mark)); }