Question

我有2个名为Post和PostDetails的实体类。两者都使用MapsId与OneToOne关系进行映射，并共享主键，如下所示。

Post.java

@Entity
@Table(name = "post")
@Data
public class Post implements Serializable
{
    private static final long serialVersionUID = -6698422774799518217L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NaturalId
    @Column(name = "title")
    private String title;

    @OneToOne(mappedBy = "post", cascade = CascadeType.ALL, fetch = FetchType.LAZY, optional = false)
    private PostDetail detail;

}

PostDetail.java

@Entity
@Table(name = "post_detail")
@Data
public class PostDetail implements Serializable
{
    private static final long serialVersionUID = -6699482774799518217L;

    @Id
    private Long id;

    @Column(name = "created_on")
    private Date createdOn;

    @Column(name = "created_by")
    private String createdBy;

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    @JoinColumn(name = "id")
    @JsonIgnore
    private Post post;

}

PostController.java

@RestController
@RequestMapping("/api/v1/post")
public class PostController
{
    private final PostRepository postRepository;

    private final PostDetailRepository postDetailRepository;

    public PostController(PostRepository postRepository, PostDetailRepository postDetailRepository)
    {
        this.postRepository = postRepository;
        this.postDetailRepository = postDetailRepository;
    }

    @GetMapping(path = "/create")
    public List<Post> createAndGetPosts()
    {

        Post post=new Post();
        post.setId(new Random().nextLong());
        post.setTitle("First Post");
        post=postRepository.saveAndFlush(post);

        PostDetail postDetail =new PostDetail();
        postDetail.setCreatedBy("Admin");
        postDetail.setCreatedOn(Date.from(Instant.now()));
        postDetail.setPost(post);
        postDetailRepository.saveAndFlush(postDetail);

        return postRepository.findAll(Sort.by(Sort.Direction.DESC,"id"));
    }


}

在Post Controller类中，我创建Post对象（将其保存为DB），然后将其传递给PostDetail对象，然后使用Spring Data JPA将其保存到数据库中。一切正常。但是，当我立即通过postRepository.findAll(Sort.by(Sort.Direction.DESC,"id"));方法获取记录列表时，我在Post内收到PostDetail对象的null值，如下所示。

回复：

[
  {
    "id": 2,
    "title": "First Post",
    "detail": null
  },
  {
    "id": 1,
    "title": "Post1",
    "detail": {
      "id": 1,
      "createdOn": "2019-06-21T03:31:43.000+0000",
      "createdBy": "Admin"
    }
  }
]

但是当我再次从前端发送该列表的请求时，我得到了正确的响应。我试图将flush语句和第二个findAll（）语句放在请求之前，但没有任何效果。

Answer 1

之所以会这样，是因为您收到了与saveAndFlush返回的实例完全相同的实例，并存储在post变量中。

执行Post.detail时，Hibernate不会更新postDetail.setPost(post)。

要修复此问题，您可以在保存后手动设置detail或从缓存中逐出Post实例，这会迫使休眠状态从数据库重新加载它。

使用MapsId映射的OneToOne关系时，findAll（）方法不返回最近插入的记录

1 个答案: