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;

    @CreatedDate
    private Instant createdAt;
    @LastModifiedDate
    private Instant updatedAt;
    @CreatedBy
    private UUID createdBy;

    @Override
    public String toString() {
        return String.format("User{id = %d," +
                "UserName = %s," +
                "FirstName = %s," +
                "LastName = %s," +
                "Age = %d," +
                "Email = %s," +
                "Address = %s," +
                "Phone Number = %s}", id, username, firstName, lastName, age, email,address, phone);
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if(o==null || getClass()!=o.getClass()) return false;
        User user = (User) o;
        return username.equals(user.username);
    }
    @Override
    public int hashCode() {
        return Objects.hash(username);
    }
}

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;

    @Override
    public String toString() {
        return "Phone [id = " + id + ", phone = " + number + "]";
    }
    @Override
    public int hashCode() {
        return Objects.hash(number);
    }
    @Override
    public boolean equals(Object obj) {
        if(this == obj) return true;
        if(obj == null) return false;
        if(getClass() != obj.getClass()) return false;
        Phone phoneNumber = (Phone) obj;
        return number.equals(phoneNumber.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;

    @Override
    public String toString() {
        return String.format("User{id = %d," +
                "UserName = %s," +
                "FirstName = %s," +
                "LastName = %s," +
                "Age = %d," +
                "Email = %s," +
                "Address = %s," +
                "Phone Number = %s}", id, username, firstName, lastName, age, email,address, phone);
    }
}

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;

    //    ***********************************************************
    //    ******************* GETTING ALL USERS *********************
    //    ***********************************************************
    @Override
    @Transactional(readOnly = true)
    public List<UserResponse> getAllUsers() {
        return userRepository.findAll()
                .stream()
                .map(this::buidUserResponse)
                .collect(Collectors.toList())
                ;
    }

    @NonNull
    private UserResponse buidUserResponse(@NonNull User user) {
        return new UserResponse()
                .setId(user.getId())
                .setUsername(user.getUsername())
                .setFirstName(user.getFirstName())
                .setLastName(user.getLastName())
                .setEmail(user.getEmail())
                .setAge(user.getAge())
                .setAddress(new AddressResponse()
                        .setCountry(user.getAddress().getCountry())
                        .setCity(user.getAddress().getCity())
                        .setStreet(user.getAddress().getStreet())
                        .setBuildingNumber(user.getAddress().getBuidingNumber())
                        .setAppt(user.getAddress().getAppt())
                )
                .setPhone(new PhoneResponse().setPhone(user.getPhone().getNumber()));
    }

    //    ***********************************************************
    //    ******************** FIND USER BY ID **********************
    //    ***********************************************************
    @Override
    @NonNull
    @Transactional(readOnly = true)
    public UserResponse findUserById(@NonNull Long id) {
        return userRepository.findById(id).map(this::buidUserResponse).orElseThrow(()->new EntityNotFoundException("User not found"));
    }

    //    ***********************************************************
    //    ******************* FIND USER BY PHONE ********************
    //    ***********************************************************
    @NonNull
    @Transactional(readOnly = true)
    @Override
    public UserResponse getUserByPhoneNumber(String phoneNumber) {
//        Phone phone = phoneServiceImpl.getPhoneByNumber(phoneNumber);
//        System.out.println(phone);
//        UserResponse user = userRepository.getUserByPhone(phone);
//        System.out.println(user);
        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(produces = APPLICATION_JSON_VALUE)
    public List<UserResponse> getAllUsers() {
        log.debug("Getting all users");
        return userService.getAllUsers();
    }

    @GetMapping(value = "/{userId}", produces = APPLICATION_JSON_VALUE)
    public UserResponse getUserById(@PathVariable Long userId) {
        return userService.findUserById(userId);
    }

    @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"
}

then I found that I can not get phones by Id or phonenumber. After how I creted PhoneRepository which extends JpaRepository<Phone, Long> and then service and controller

@Service
@RequiredArgsConstructor
public class PhoneServiceImpl implements PhoneService {

    private final PhoneRepository phoneRepository;

    @Override
    @Transactional(readOnly = true)
    public PhoneResponse getPhoneByNumber(@NotNull String phoneNumber) {
        return phoneRepository.getPhoneByNumber(phoneNumber);
    }

    private PhoneResponse buildPhoneResponse(Phone phone) {
        return new PhoneResponse().setPhone(phone.getNumber());
    }

    @Override
    @Transactional(readOnly = true)
    public PhoneResponse findPhoneById(@NotNull Long phoneId) {
        return phoneRepository.findById(phoneId).map(this::buildPhoneResponse).orElseThrow(
                ()->new EntityNotFoundException("User not found")
        );
    }

    @Override
    @Transactional(readOnly = true)
    public List<PhoneResponse> getAllPhone() {
        return phoneRepository.findAll().stream().map(this::buildPhoneResponse).collect(Collectors.toList());
    }
}

and controller:

@RestController
@RequestMapping("/api/v1/phones")
@RequiredArgsConstructor
public class PhoneController {
    private final PhoneServiceImpl phoneService;

    @GetMapping(produces = APPLICATION_JSON_VALUE)
    public List<PhoneResponse> getAllPhones() {
        return phoneService.getAllPhone();
    }

    @GetMapping(value = "/number/{phoneNumber}", produces = APPLICATION_JSON_VALUE)
    public PhoneResponse getPhone(@PathVariable String phoneNumber) {
        return phoneService.fetPhoneByNumber(phoneNumber);
    }

    @GetMapping(value = "/id/{phoneId}", produces = APPLICATION_JSON_VALUE)
    public PhoneResponse getPhoneById(@PathVariable Long phoneId) {
        return phoneService.findPhoneById(phoneId);
    }
}

I am able to look for only list of phone numbers. I can not find by Number…I still 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"
}