No converter found capable of converting from type to type #2

Question

I know it's another similar question, but I can't answer it myself, that's why I'm writing to you for help.

I try to create my own @Query and returns a conversion error on two occasions. My guess is there is a problem with the service, but this is where my knowledge ends.

Here is my code:

1. Main entity

    @Data
    @Entity
    @Table(name = "users")
    public class User {
   
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String name;
    private String city;
    private  Date startDate;
    private boolean stat;
   
    public User() {
    }
   
    public User(String name, String city, Date startDate, boolean stat) {
        this.name = name;
        this.city = city;
        this.startDate = startDate;
        this.stat = stat;
     }
    }
   

2.Second model

public class UserName {
    private String firstname;
    public UserName() {
    }
    public UserName(String firstname) {
        this.firstname = firstname;
    }
    public String getFirstname() {
        return firstname;
    }
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }
}

3.Third model

public class UserCount {

    private String city;
    private int count;

    public UserCount() {
    }
    public UserCount(String city, int count) {
        this.city = city;
        this.count = count;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
}

4. Repository

   @Repository public interface UserRepository extends JpaRepository<User, Long> {

    @Query("select p from User p")  //1.it's work
    List<User> getAll();
   
    @Query("select u from User u where u.name like %?1")  //2.it's work
    List<User> findByFirstnameEndsWith(String firstname);
   
    @Query("select u.name from User u ")  //3. don't work
    List<UserName> getNameUsers();
   
    // this SQL working in database console H2
    // SELECT city, count(*) FROM USERS  WHERE stat = true GROUP BY  city
    @Query("select u.city, count (u) from User u where u.stat = true group by u.city")  //3. don't work
    List<UserCount> getOwnQuery();
   

   }

5. Service

   @Service public class UserService { @Autowired private UserRepository repo;

    public List<UserName> getN (){
        return repo.getNameUsers();
    }
   
    public List<UserCount> getC(){
        return repo.getOwnQuery();
    }
   

   }

6. Controller

   @Controller public class MyController {

    @Autowired
    private UserRepository repo;
    @Autowired
    private UserService repoService;
   
    @GetMapping("/") //1.it's work
    ResponseEntity<List<User>> getAllCity(Pageable page){
        return ResponseEntity.ok(repo.getAll());
    }
    @GetMapping("/s") //2.it's work
    ResponseEntity<List<User>> getAllUsers(Pageable page){
        return ResponseEntity.ok(repo.findByFirstnameEndsWith("Seba"));
    }
    @GetMapping("/f") ///3.don't work
    ResponseEntity<List<UserName> >getUsersName(Pageable page){
        return ResponseEntity.ok(repoService.getN());
    }
    @GetMapping("/c") ///4.don't work
    ResponseEntity<List<UserCount> >getUsersCount(Pageable page){
        return ResponseEntity.ok(repoService.getC());
    }
   

   }

It also adds source code on GitHub

sorry i didn't add the error code

Answer 1

Use constructor with NEW keyword in @Query to get List<UserName>

@Query("select NEW com.sub.model.UserName(u.name) from User u ")
List<UserName> getNameUsers();

And do the same for List<UserCount>

@Query("select NEW com.sub.model.UserCount(u.city, count(u)) from User u where u.stat = true group by u.city")
List<UserCount> getOwnQuery();