Why I can not look for entities between joined tables?

Question

I have two entities User and Phone.

User Entity:

@Getter
@Setter
@Accessors(chain = true)
@Entity
@Table(name = "user_table")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;
    @Column(name = "username", unique = true, nullable = false)
    @NonNull
    private String username;
    @Column(name = "firstname")
    @NonNull
    private String firstName;
    @Column(name = "lastname")
    @NonNull
    private String lastName;
    @Column(name = "age")
    @NonNull
    private Integer age;
    @Column(name = "email", nullable = false, unique = true)
    @NonNull
    private String email;
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id", foreignKey = @ForeignKey(name = "fk_user_address_id"))
    private Address address;
    @OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "phone_number", foreignKey = @ForeignKey(name = "fk_user_phone_number"))
    private Phone phone;
}

Phone Entity :

@Getter
@Setter
@Accessors(chain = true)
@Entity
@Table(name = "phone_table")
public class Phone {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "phone_number", unique = true, nullable = false)
    @NonNull
    private String number;
}

Also I created a DTO classes of these Entities.

@Data
@Accessors(chain = true)
public class CreateUserRequest {
    private Long userId;
    private String username;
    private String firstName;
    private String lastName;
    private Integer age;
    private String email;
    private CreatePhoneRequest phone;
    private CreateAddressRequest address;
}

@Data
@Accessors(chain = true)
public class UserResponse {
    private Long id;
    private String username;
    private String firstName;
    private String lastName;
    private String email;
    private int age;
    private PhoneResponse phone;
    private AddressResponse address;
    }
}

and

@Data
@Accessors(chain = true)
public class CreatePhoneRequest {
    private String phone;
}
@Data
@Accessors(chain = true)
public class PhoneResponse {
    private String phone;
}

Then UserRepository extends JpaRepository<Long, User> where I findUserByPhone_Number(String phonenumber)

in service I make the logic for looking for users:

@Service
@RequiredArgsConstructor
public class UserServiceImpl implements UserService {
    private final UserRepository userRepository;
    private final PhoneServiceImpl phoneServiceImpl;

    //    ***********************************************************
    //    ******************* FIND USER BY PHONE ********************
    //    ***********************************************************
    @NonNull
    @Transactional(readOnly = true)
    @Override
    public UserResponse getUserByPhoneNumber(String phoneNumber) {
        return userRepository.findUserByPhone_Number(phoneNumber);
    } 
}

and UserController for making requests:

@RestController
@RequestMapping("/api/v1/users")
@RequiredArgsConstructor
public class UserController {
    private final UserServiceImpl userService;
    private final Logger log = LoggerFactory.getLogger(UserController.class);

    @GetMapping(value = "/phonenumber/{number}", produces = APPLICATION_JSON_VALUE)
    public UserResponse getUserByPhoneNumber(@PathVariable String number) {
        UserResponse user = userService.getUserByPhoneNumber(number);
        System.out.println(user);
        return user;
    }
}

And I can get list of users, I can get user by ID..... but when I try to get user by phoneNumber (Joined Table), I receive :

{
    "message": "Specified result type [com.app.apringlearn.app.ResponseRequest.UserResponse] did not match Query selection type [com.app.apringlearn.app.Enteties.User] - multiple selections: use Tuple or array"
}

Answer 1

just make your getUserByPhoneNumber return User but not UserResponse

@NonNull
    @Transactional(readOnly = true)
    @Override
    public User getUserByPhoneNumber(String phoneNumber) {
        return userRepository.findUserByPhone_Number(phoneNumber);
    } 

and change all the linking classes accordingly.

it should work as you expect...