java - Spring JPA 一对多无限递归

Question

我试图返回 JPA 数据(当然，转换为 DTO)，其中具有 @OneToMany 和 @ManyToOne 双向关系。我目前正在申请东西fix 。问题是输出是递归的。评论有帖子，有评论，然后有帖子(评论 -> 帖子 -> 评论 -> 等等..)。

我只想拥有这样的东西

{
    "post_id": 1
    "user": {
        // user data
    },
    "description": "some description",
    "images": "{images,images}",
    "tags": "{tags, tags}",
    "comments": [
     {
        //some comments data

     },
     {
        //some comments data
     }
    ]
    "lastUpdated": "2020-04-08T14:23:18.000+00:00"
}

这是我的代码

这是我的 Posts.class

@Data
@Entity
@Table(name = "posts")
@EntityListeners(AuditingEntityListener.class)
public class Posts {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "post_id")
    private Long post_id;

    @ManyToOne
    @JoinColumn(name = "user_id", nullable = false)
    private Users user;

    @Column(name = "description")
    private String description;

    @Column(name="images")
    private String images;

    @Column(name="tags")
    private String tags;

    @OneToMany(
        fetch = FetchType.LAZY,
        mappedBy = "post",
        cascade = CascadeType.ALL,
        orphanRemoval = true
    )
    @JsonIgnoreProperties(value = { "comments" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
    //@JsonManagedReference
    private List<Comments> comments;


    @LastModifiedDate
    @Column(name = "last_updated")
    private Date lastUpdated;


    public void addComments(Comments comment) {
        this.comments.add(comment);
    }
}

这是我的 PostDTO.class

@Data
public class PostDTO {

    private Long post_id;
    private UserDTO user;
    private String description;
    private String images;
    private String tags;
    private List<CommentsDTO> comments;
    private Date lastUpdated;


}

这是我的 Comments.class

@Data
@Entity
@Table(name = "comments")
@EntityListeners(AuditingEntityListener.class)
public class Comments {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name="comment_id")
    private Long comment_id;

    @OneToOne
    @JoinColumn(name = "user_id")
    private Users user;

    @Column(name = "description")
    private String description;

    @Column(name="images")
    private String images;

    @ManyToOne
    @JoinColumn(name ="post_id" , nullable = false)
    @JsonIgnoreProperties(value = { "post" ,"hibernateLazyInitializer", "handler" }, allowSetters = true)
    //@JsonBackReference
    private Posts post;

    @Column(name="last_updated")
    @LastModifiedDate
    private Date lastUpdated;

}

这是我的 CommentsDTO.class

@Data
public class CommentsDTO {

    private Long comment_id;

    private UserDTO user;

    private String description;

    private PostDTO post;

    private String images;

    private Date lastUpdated;
}

这是我的 REST Controller

@GetMapping
public @ResponseBody ResponseEntity<List<PostDTO>>  getAll() throws Exception {

    return new ResponseEntity<List<PostDTO>>(service.getAll(), HttpStatus.OK);
}

这是我的服务

public List<PostDTO> getAll() throws Exception  {
    return repo.findAll()
               .stream()
               .map(this::convert)
               .collect(Collectors.toList());
}

private PostDTO convert(Posts e) {
    return  mapper.map(e, PostDTO.class);
}

希望有人能解答我的问题。这次有点输了。

Answer 1

问题是，当您将 Post 转换为 PostDTO 时，然后通过使用 ModelMapper，它会为 PostDTO 调用 Post 的所有字段的 getter。所以这递归地发生了mapper.map(e, PostDTO.class)

因此，只需从 CommentDTO 中删除 private PostDTO post 即可，那么 modelmapper 不要尝试设置 PostDTO->comment->post 字段。而且 DTO 中不需要双向关系。 DTO 就是您想要在响应中显示的内容。