找不到能够从类型转换为类型#2的转换器

Question

我知道这是另一个类似的问题，但我自己无法回答，这就是我写信给你寻求帮助的原因。

我尝试创建自己的@Query，并在两种情况下返回一个转换错误。我的猜测是服务有问题，但这是我的知识结束。

下面是我的代码：

>

主实体

 @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.第二种模式

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.第三种模式

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;
    }
}

存储库

@Repository public interface UserRepository extends jparepository {

 @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();

}

服务

@Service public class UserService{@AutoWired private UserRepository Repo

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

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

}

控制器

@Controller公共类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());
 }

}

它还在GitHub上添加了源代码

对不起，我没有添加错误代码

Answer 1

在@Query中使用带有new关键字的构造函数获取列表

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

并对列表 执行相同的操作

@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();