Courses API Controllers

@RestController
@RequestMapping("/api/courses")
public class CourseController {
    @Autowired
    private CourseRepository courseRepository;
    
    @PostMapping
    public Course createCourse(@RequestBody Course course) {
        return courseRepository.save(course);
    }
    
    @GetMapping
    public List<Course> getAllCourses() {
        return courseRepository.findAll();
    }
    
    @GetMapping("/{id}")
    public Course getCourse(@PathVariable Long id) {
        return courseRepository.findById(id).orElseThrow();
    }
    
    @DeleteMapping("/{id}")
    public void deleteCourse(@PathVariable Long id) {
        courseRepository.deleteById(id);
    }
}

@RestController
@RequestMapping("/api/instances")
public class InstanceController {
    @Autowired
    private InstanceRepository instanceRepository;
    
    @PostMapping
    public Instance createInstance(@RequestBody Instance instance) {
        return 
        instanceRepository.save(instance);
    }
    
    @GetMapping("/{year}/{semester}")
    public List<Instance> getInstances(@PathVariable Integer year, @PathVariable Integer semester) {
        return instanceRepository.findByYearAndSemester(year, semester);
    }
    
    @GetMapping("/{year}/{semester}/{id}")
    public Instance getInstance(@PathVariable Integer year, @PathVariable Integer semester, @PathVariable Long id) {
        return instanceRepository.findByIdAndYearAndSemester(id, year, semester).orElseThrow();
    }
    
    @DeleteMapping("/{year}/{semester}/{id}")
    public void deleteInstance(@PathVariable Integer year, @PathVariable Integer semester, @PathVariable Long id) {
        instanceRepository.deleteByIdAndYearAndSemester(id, year, semester);
    }
}