在spring数据jpa中获取非表实体的数据

Question

我有列 id、mname、firstname、lastname、age（5 列）的用户表 使用 spring data jpa 我只需要获取 id、firstname、age（只有 3 列）

userentity 在 user.java 之下

 @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 colsole 中出现以下错误：

org.springframework.core.convert.ConverterNotFoundException: 否 发现能够从类型 [java.math.BigInteger] 转换的转换器 输入 [com.user.entity.User2]

检查代码时出现错误：

无法从类型 [java.lang.Object[]] 转换为类型 [com.user.entity.User2] 为值 '{403, firstnnnnnn, 26}';

有没有办法将值映射到 user2（非表实体）？

Answer 1

你应该使用projections:

Interface based:

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

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

Class based (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);
}