Spring: Unique Id validator without using Hibernate

Question

What is the best way to check by validator to don't have duplicate ID when you do a POST?

I tried to create a custom validator but I get always an Internal Server Error

{ "timestamp": "2020-04-25T14:37:19.158+0000", "status": 500, "error": "Internal Server Error", "message": "HV000030: No validator could be found for constraint 'com.omega.mtest.validator.IdConstraint' validating type 'java.lang.Integer'. Check configuration for 'id'", "path": "/user" }

This is my model class

    public class User {

        @IdConstraint
        @Min(value = 1, message = "ID can't be zero or null")
        @Max(value = 1000000, message = "We collect a billion records")
        private int id;



        @Pattern(regexp = "^[a-zA-Z ]*$", message = "Input doesn't match for a full name")
        private String name;

        @Min(value = 10)
        @Max(value = 120, message = "We didn't expect that age")
        private int age;

        @Pattern(regexp = "^[a-zA-Z ]*$", message = "Input doesn't match for a city name")
        private String city;

        public User(int id, String name, int age, String city) {
            this.id = id;
            this.name = name;
            this.age = age;
            this.city = city;
        }

       //getters
    }

Custom Validator Interface:

@Constraint(validatedBy = UserValidator.class)
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RUNTIME)
public @interface IdConstraint {

    String message() default "The input list cannot contain two ugual IDs";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

Class implementation of the interface

public class UserValidator implements ConstraintValidator<IdConstraint, List<User>> {

    @Override
    public void initialize(IdConstraint constraintAnnotation) {

    }

    @Override
    public boolean isValid(List<User> users, ConstraintValidatorContext context) {
        if (users.size() == 1) {
            return true;
        } else {
            for (int i = 0; i < users.size(); i++) {
                for (int j = 0; j < users.size(); j++) {
                    if (i != j) {
                        if (users.get(i).getId() == users.get(j).getId()) {
                            return true;
                        }
                    }
                }
            }
            return false;
        }
    }

Controller class:

@Validated
@RestController
public class UsersController {

    @Autowired
    public UserService userService;

    @RequestMapping(value = "/user", method = RequestMethod.POST)
    public ResponseEntity<User> createUser(@Valid @RequestBody User user) {
        return new ResponseEntity<>(userService.createUser(user), HttpStatus.CREATED);
    }

    @ExceptionHandler(ConstraintViolationException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    ResponseEntity<String> handleConstraintViolationException(ConstraintViolationException e) {
        return new ResponseEntity<>("Not valid due to validation error: " + e.getMessage(), HttpStatus.BAD_REQUEST);
    }

    @RequestMapping(value = "/users", method = RequestMethod.GET)
    public List<User> getUsers() {
        return userService.getAllUsers();
    }

    @RequestMapping(value = "/user/{id}", method = RequestMethod.GET)
    public User getUserById(@PathVariable int id) {
        return userService.findUserById(id);
    }
}

UserService

public interface UserService {

    List<User> getAllUsers();

    User createUser(User user);

    User findUserById(int id);

    List<User> list();
}

Repo

@Component
public class UserRepository implements UserService {

    private List<User> users;

    public UserRepository() {
        users = new ArrayList<>();
    }

    @Override
    public List<User> getAllUsers() {
        return users.stream().collect(Collectors.toList());
    }

    @Override
    public User createUser(User user) {
        users.add(user);
        return user;
    }


    @Override
    public User findUserById(int id) {
        return users.stream()
                .filter(t -> t.getId() == id)
                .findAny()
                .orElse(null);
    }

    @Override
    public List<User> list() {
        return users;
    }
}

Answer 1

I did this way, and it's working:

  @RequestMapping(value = "/user", method = RequestMethod.POST)
public ResponseEntity<User> createUser(@Valid @RequestBody User user) {
    Optional<User> check = userService.findUserById(user.getId());
    if (check.isPresent()) {
        return new ResponseEntity<>(userService.createUser(user), HttpStatus.CREATED);
    }
    return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
}



@RequestMapping(value = "/user/{id}", method = RequestMethod.GET)
    public ResponseEntity<User> getUserById(@PathVariable int id) {
        if (userService.findUserById(id).isPresent()) {
            return new ResponseEntity<>(userService.findUserById(id).get(), HttpStatus.OK);
        }
        return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
    }

Answer 2

Your validator signature is not correct.

You're not validate list of users here but an Integer .

Like this

public class UserIdValidator implements ConstraintValidator<IdConstraint, Integer> {

Then you have to ask your service if the id is already used.

public class UserIdValidator implements ConstraintValidator<IdConstraint, Integer> {

    @Autowired
    Private UserService userService;

    @Override
    public void initialize(IdConstraint constraintAnnotation) {

    }

    @Override
    public boolean isValid(Integer id, ConstraintValidatorContext context) {
         return !userService.existsById(id);
        }
    }

Answer 3

First of all you are using @IdConstraint in the wrong place means on private int id. You have to put this on List<User>. And your validator work when you have list of user and any on two user don't have same id in request body. You can solve this 2 way.

Checking is service:

Here in post endpoint you are using one user as a request body. So you can check if id exists in the database in service using getById() of the repository. If exist then raise exception otherwise insert.

User user= userRepository.getById(user.getId());
if (ObjectUtils.isEmpty(user)) {
  throw new UserNotFoundException();
}

Using Validator:

It is not a better approach to call repository in validator function. But still, you want you can do like this.

public class UserIdValidator implements ConstraintValidator<IdConstraint, Integer> {

    @Autowired
    Private UserService userService;

    @Override
    public void initialize(IdConstraint constraintAnnotation) {

    }

    @Override
    public boolean isValid(Integer id, ConstraintValidatorContext context) {
      User user= userService.findUserById(id);
      if (ObjectUtils.isEmpty(user)) {
        return false;
      }
      return true;
    }
}