java - Spring Boot get请求未使用@OneToMany获取第三级对象

Question

我的数据库表设计如下。

使用这种结构，使用 Springboot，我无法获取 TABLE-1 到 TABLE-3 的所有子元素

下面是相同的实体类

表-1 (SDKMainCollection.java)

@Entity
@Table(name="sdkmaincollection")
public class SDKMainCollection {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String sdkgroupname;
    @JsonIgnore
    @OneToMany(mappedBy = "sdkcollectionobj", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<SDKCollection> sdkcollection;

    public SDKMainCollection() {
    }

    public SDKMainCollection(int id,String sdkGroupName) {
        this.id= id;
        this.sdkgroupname =sdkGroupName;
    }

    public SDKMainCollection(String sdkGroupName) {
        this.sdkgroupname =sdkGroupName;
    }
    //Getters and Setters
}

表2(SDKCollection.java)

@Entity
@Table(name="sdkcollection")
public class SDKCollection {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String sdktitle;
    private String sdkid;
    private String sdkresourceid;
    private String sdkdescription;
    private String sdkimageName;
    @JsonIgnore
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "sdkmaincollection_id")
    private SDKMainCollection sdkcollectionobj;
    @JsonIgnore
    @OneToMany(mappedBy = "sdkcolsubobj", cascade = CascadeType.ALL, fetch=FetchType.LAZY) 
    private Set<Ads> ads;

    public SDKCollection() {
    }
    public SDKCollection(int id, String sdkTitle, String sdkId, String sdkresourceId, String sdkdescription,
            String sdkimageName,SDKMainCollection sdkObj) {
        this.id = id;
        this.sdktitle = sdkTitle;
        this.sdkid = sdkId;
        this.sdkresourceid = sdkresourceId;
        this.sdkdescription = sdkdescription;
        this.sdkimageName = sdkimageName;
        this.sdkcollectionobj = sdkObj;
    }
    public SDKCollection(String sdkTitle, String sdkId, String sdkresourceId, String sdkdescription,
            String sdkimageName,SDKMainCollection sdkObj) {

        this.sdktitle = sdkTitle;
        this.sdkid = sdkId;
        this.sdkresourceid = sdkresourceId;
        this.sdkdescription = sdkdescription;
        this.sdkimageName = sdkimageName;
        this.sdkcollectionobj = sdkObj;
    }
    //Getters and Setters
}

表 3 (Ads.java)

@Entity
@Table(name="ads")
public class Ads {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String adtitle;
    private String adtag;
    private String adtype;
    private String imagename;
    private String controlid;
    @JsonIgnore
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "sdkcollection_id")
    private SDKCollection sdkcolsubobj;

    public Ads() {

    }
    public Ads(int id, String adTitle, String adTag, String adType, String imageName, String controlID,
            SDKCollection sdkcollection     
            ) {
        this.id = id;
        this.adtitle = adTitle;
        this.adtag = adTag;
        this.adtype = adType;
        this.imagename = imageName;
        this.controlid = controlID;
        this.sdkcolsubobj = sdkcollection;
    }
    public Ads(String adTitle, String adTag, String adType, String imageName, String controlID
            ,SDKCollection sdkcollection) {
        this.adtitle = adTitle;
        this.adtag = adTag;
        this.adtype = adType;
        this.imagename = imageName;
        this.controlid = controlID;
        this.sdkcolsubobj = sdkcollection;
    }
    //Getters and Setters
}

下面是我用于获取元素的 Controller 类

@RestController
@RequestMapping("/api/sdk/")
@CrossOrigin
public class GetSDKController {
    @Autowired
    private SDKMainCollectionRepo sdkMainCollectionRepo;
    @Autowired
    private SDKCollectionRepo sdkCollectionRepo;
    @Autowired
    private AdsRepo adsRepo;
    @GetMapping("/getAllSDKs")
    public List<SDKMainCollection> getAllSDK(){
        sdkDataMapper = new SDKDataMapper(sdkMainCollectionRepo,sdkCollectionRepo,adsRepo);
        List<SDKMainCollection> totalResp  = (List<SDKMainCollection>) sdkMainCollectionRepo.findAll();
        System.out.println("getAllSDK = totalResp "+totalResp);

        //NOT GETTING WHAT IS EXPECTED

        return totalResp;
    }
}

以下是我的期望，但我收到 Stackoverflow 错误

Stackoverflow 错误日志:

java.lang.StackOverflowError: null
    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_131]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKMainCollection.toString(SDKMainCollection.java:59) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKCollection.toString(SDKCollection.java:118) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_131]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKMainCollection.toString(SDKMainCollection.java:59) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKCollection.toString(SDKCollection.java:118) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_131]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKMainCollection.toString(SDKMainCollection.java:59) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at com.dvservices.models.SDKCollection.toString(SDKCollection.java:118) ~[classes/:na]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_131]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_131]
    at java.util.AbstractCollection.toString(Unknown Source) ~[na:1.8.0_131]
    at org.hibernate.collection.internal.PersistentSet.toString(PersistentSet.java:328) ~[hibernate-core-5.3.7.Final.jar:5.3.7.Final]

我猜问题可能是获取最后一个数组并导致 Stackoverflow 错误。

编辑:

此问题是否是由于位于层次结构中间的同一个 SDKCollection 类中同时存在 OneToMany 和 ManyToOne 造成的？

public class SDKCollection {

       ........
       @JsonIgnore
       @ManyToOne(fetch = FetchType.LAZY)
       @JoinColumn(name = "sdkmaincollection_id")
       private SDKMainCollection sdkcollectionobj;

       @JsonIgnore
       @OneToMany(mappedBy = "sdkcolsubobj", cascade = CascadeType.ALL, fetch=FetchType.LAZY) 
       private Set<Ads> ads;

Answer 1

您缺少 @JsonBackReference 注释，这就是您收到 stackoverflow 错误的原因。@JsonIgnore 并不是为了解决无限递归问题而设计的，它只是忽略被序列化或反序列化的带注释的属性。

添加位置

1. 在 SDKCollection.java 中私有(private) SDKMainCollection sdkcollectionobj;对 SDKMaincollection 的反向引用，
2. 在 Ads.java 中私有(private) SDKCollection sdkcolsubobj 对 SDKCollection 的反向引用

上面两者都应该用@JsonBackReference注释希望有帮助。