在Spring数据jpa中获取非表实体的数据

Question

我有用户表，列id， mname， firstname， lastname， age（5列）使用Spring data jpa我只需要获取id， firstname， age（只有3列）

实用性低于user.java

 @Entity
    @Table(name = "user")
   public class User implements Serializable {

    private static final long serialVersionUID = -3009157732242241606L;
    @Id
    private long id;

    @Column(name = "mname")
    private String mName;

    @Column(name = "firstname")
    private String firstName;

    @Column(name = "firstname")
    private String firstName;

    @Column(name = "lastname")
    private String lastName;

    @Column(name="age")
    private int age;

    //constructor with fileds


user2.java contains the fileds

private Long id;
private String firstname;
private int age;

//getter and setter

UserRepository.java

public interface UserRepository extends CrudRepository<User, Long> {
@Query(value="SELECT usr.id as id,usr.firstname as firstName, usr.age as age FROM user usr WHERE usr.id=?1", nativeQuery=true)
List<User2> getUserDetailsByUserId(Long id);
}

在科尔索勒中收到以下错误：

org.springframework.core.convert.ConverterNotFoundException：找不到能够从类型[java.math.BigInteger]转换为类型[com.user.entity.User2]的转换器

检查代码时得到错误：

无法将值“{403，firstnnnnnnn，26}”从类型[java.lang.Object[]]转换为类型[com . user . entity . user 2]；

有没有办法把值映射到user2(非表实体)？

Answer 1

您应该使用投影：

基于接口:

public interface UserProjection {
    Long getId();
    String getFirstname();
    Integer getAge();
}

public interface UserRepository extends CrudRepository<User, Long> {
    List<UserProjection> findById(Long id);
}

基于类别(DTO):

@Value // It's Lombok annotation
public class UserDto {
    Long id;
    String firstname;
    Integer age;
}

public interface UserRepository extends CrudRepository<User, Long> {
    List<UserProjection> findById(Long id);
    List<UserDto> getById(Long id);
}