Spring JPA联接

Question

我是spring框架的初学者,

我在存储库和SQL连接部分面临一些问题。我想使用联接查询从两个表中获取详细信息。

请找到下面的错误

select c.created_at , c.updated_at , p.content,c.text , p.id , c.posting_dummy 
from     post p join  comment c 
on  p.id = c.posting_dummy;

存储库：

@Repository
public interface JoinRepository  extends JpaRepository<JoinQuery, Long>
{
@Query(value = " select  c.created_at , c.updated_at , p.content,c.text , p.id , c.posting_dummy "
            + "  from   post p join  comment c   on  p.id = :id ", nativeQuery = true)
public  List<JoinQuery> queryBy(Long id);
}

POJO：

public class JoinQuery 
{
private Long id;
private Date createdAt;
private Date updatedAt;
private String content;
private String text;
private  Post posting_dummy;

// Getter and Setter for fields       
}

控制器：

@RestController
public class CommentController {

@Autowired
private CommentRepository commentRepository;

@Autowired
private PostRepository postRepository;

@Autowired
private JoinRepository joinRepository;

@GetMapping("/posts/{postId}/comments")
public List<JoinQuery>  getAllCommentsByPostId(@PathVariable (value = "postId") Long postId
                                                    ) 
{
System.out.println("hi am here ");
return joinRepository.queryBy(postId);
}

}

Answer 1

公共类JoinQuery需要@Entity注释。

@Entity
public class JoinQuery 
{
private Long id;
private Date createdAt;
private Date updatedAt;
private String content;
private String text;
private  Post posting_dummy;

// Getter and Setter for fields       
}

查询也不能是本机查询使用：

@Query(value = " select  new <package of jpaquery>.JoinQuery(c.created_at , c.updated_at , p.content,c.text , p.id , c.posting_dummy) "
            + "  from   post p.c")

顺便说一句：不要使用实体作为控件的返回值。了解3Tier体系结构