java - 子对象具有父对象作为属性 JPA 导致无尽的 JSON

Question

我在父对象 CommentTarget 中定义了以下内容:

// bi-directional many-to-one association to EmployerDetails
@OneToMany(mappedBy = "commentTarget", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Comment> comments;

这在子评论中定义:

@ManyToOne(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH} )
@JoinColumn(name = "comment_target_id")
private CommentTarget commentTarget;

但是，当我从目标获取列表并以 JSON 形式返回时:

@RestController
@RequestMapping("/ticketV2")
public class TicketV2Controller {

    @Autowired
    CommentTargetService commentTargetService;

    @RequestMapping(value = "/{ticketId}/comments", method = RequestMethod.GET)
    public List<Comment> getTicketComments(@PathVariable(value="ticketId") String id,
                                    @RequestParam String type){

        CommentTarget commentTarget = commentTargetService.findByTargetIdAndTargetType(Long.valueOf(id), TargetName.valueOf(type));
        List<Comment> commentsList = commentTarget.getComments();

        return commentsList;
    }

它会崩溃，因为它保留了对目标的引用，然后是其中的列表等等:

[
{
    "id": 997,
    "commentedBy": 1,
    "commenterName": "Exchange Admin",
    "comment": "123456",
    "commentTarget": {
        "id": 703,
        "targetId": 216,
        "targetName": "TICKET",
        "created": 1586548428358,
        "updated": 1586548428358,
        "comments": [
            {
                "id": 997,
                "commentedBy": 1,
                "commenterName": "Exchange Admin",
                "comment": "123456",
                "commentTarget": {
                    "id": 703,
                    "targetId": 216,
                    "targetName": "TICKET",
                    "created": 1586548428358,
                    "updated": 1586548428358,
                    "comments": [
                        {
                            "id": 997,
                            "commentedBy": 1,
                            "commenterName": "Exchange Admin",
                            "comment": "123456",
                            "commentTarget": {
                                "id": 703,
                                "targetId": 216,
                                "targetName": "TICKET",
                                "created": 1586548428358,
                                "updated": 1586548428358,
                                "comments": [
                                    {
                                        "id": 997,
                                        "commentedBy": 1,
                                        "commenterName": "Exchange Admin",
                                        "comment": "123456",
                                        "commentTarget": {
                                            "id": 703,
                                            "targetId": 216,
                                            "targetName": "TICKET",
                                            "created": 1586548428358,
                                            "updated": 1586548428358,
                                            "comments": [

当只想返回子评论列表时，不知道如何分离两者之间的关系。

Answer 1

请注意:

1. @JsonManagedReference 是引用的前向部分 - 那个 可以正常序列化。
2. @JsonBackReference 是后面部分 引用 - 它将在序列化中被省略。

如下所示更改您的映射。

@OneToMany(mappedBy = "commentTarget", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
@JsonManagedReference
private List<Comment> comments;

@ManyToOne
@JoinColumn(name = "comment_target_id")
@JsonBackReference
private CommentTarget commentTarget;