// SQL Schema
CREATE TABLE users (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(255),
age INT
);
// Equivalent Entity Model : User.java
@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private int age;
// Getters and setters omitted for brevity
}
// Repository class that maps data from database using the Entity class User : UserRepository.java
public interface UserRepository extends JpaRepository<User, Long> {
}
// Business logic interface : UserService.java
public interface UserService {
List<User> getAllUsers();
Optional<User> getUserById(Long id);
User saveUser(User user);
void deleteUser(Long id);
}
// Business logic implementation of service that uses repository class as dependency to pull business data : UserServiceImpl.java
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserRepository userRepository;
@Override
public List<User> getAllUsers() {
return userRepository.findAll();
}
@Override
public Optional<User> getUserById(Long id) {
return userRepository.findById(id);
}
@Override
public User saveUser(User user) {
return userRepository.save(user);
}
@Override
public void deleteUser(Long id) {
userRepository.deleteById(id);
}
}
// Rest Controller class that maps url with a service business logic
@RestController
@RequestMapping("/users")
public class UserController {
@Autowired
private UserService userService;
@GetMapping
public ResponseEntity<List<User>> getAllUsers() {
List<User> users = userService.getAllUsers();
return ResponseEntity.ok(users);
}
@GetMapping("/{id}")
public ResponseEntity<User> getUserById(@PathVariable Long id) {
return userService.getUserById(id)
.map(ResponseEntity::ok)
.orElse(ResponseEntity.notFound().build());
}
@PostMapping
public ResponseEntity<User> createUser(@RequestBody User user) {
User savedUser = userService.saveUser(user);
return ResponseEntity.status(HttpStatus.CREATED).body(savedUser);
}
@DeleteMapping("/{id}")
public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
userService.deleteUser(id);
return ResponseEntity.noContent().build();
}
}public interface RoomRepository extends JpaRepository<Room, Long> {
List<Room> findAllByRoomNumberIgnoreCase(String roomNumber);
Optional<Room> findByRoomNumberIgnoreCase(String roomNumber);
// findAllBy_Field()
// findBy_Field()
// findBy_Field1_And_Field2()
}