Can not handle managed/back reference 'defaultReference': back reference type (java.util.List) not compatible with managed type (ForumAnswerReplay)

Question

Forum Answer saving time facing issue.before i saved successfully using @JsonIgnore but now i removed @JsonIgnore annonation.and added @JsonBackReference and @JsonManagedReference.

Stack Trace

java.lang.IllegalArgumentException: Can not handle managed/back reference 'defaultReference': back reference type (java.util.List) not compatible with managed type (com.tta.abcd.model.ForumAnswerReplay)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase._resolveManagedReferenceProperty(BeanDeserializerBase.java:790)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:516)
at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:296)
at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:443)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:196)
at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:26)
at com.fasterxml.jackson.databind.DeserializationContext.handleSecondaryContextualization(DeserializationContext.java:681)
at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:445)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer.findDeserializer(StdDeserializer.java:967)

Forum.java

    @Entity
    @Table(name="Forum")
    public class Forum {

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

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

    @Column(columnDefinition="varchar(1000)",name="discription")
    private String discription;

    @Column(name="postedDate")
    private Date postedDate;

    @Fetch(value = FetchMode.SELECT)
    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "forumId")
    @JsonIgnore
    private List<ForumAnswer> forumList;
    }

ForumAnswer.java

    @Entity
    @Table(name="ForumAnswer")
    public class ForumAnswer {

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

    @ManyToOne
        @JoinColumn(name = "forumId",insertable=true, updatable=true,nullable=true)
    private Forum forum;

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

    @Column(name="answerDate")
    private Date answerDate;

    @Fetch(value = FetchMode.SELECT)
    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "forumAnswerId")
    @JsonBackReference
    private List<ForumAnswerReplay> forumAnswerReplayList;

    @Transient
    private List<ForumAnswerReplay> faqReplayList;
}

ForumAnswerReplay.java

@Entity
@Table(name="ForumAnswerReplay")
public class ForumAnswerReplay {

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

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

    @Column(name="replayToAnswerDate")
    private Date replayToAnswerDate;


    @ManyToOne(fetch=FetchType.EAGER)
    @JoinColumn(name="forumAnswerId",insertable=true,updatable=true,nullable=true)
        @JsonManagedReference
    private ForumAnswer forumAnswer;

    @Transient
    private String message;
}

Controller Code:

public ForumAnswer saveForumAns(@RequestBody ForumAnswer forumAns, BindingResult bindingResult, HttpSession session,
        HttpServletRequest request, HttpServletResponse response) {
    ForumAnswer forumDetails = forumService.saveForumAns(forumAns, bindingResult, session);
    if (forumDetails != null) {
        forumDetails.setMessage("success");
    }
    else {
        forumDetails.setMessage("failed");
    }
    return forumDetails;
}

DAO:

public ForumAnswer saveForumAns(ForumAnswer forumAns, BindingResult bindingResult) {

    final Session session = getSession();
    try {
        session.beginTransaction();
        Query query = session.createQuery("UPDATE ForumAnswer set answer =:answer,"
                + "forumAnswerId =:forumAnswerId,farmerUuid =:farmerUuid, answerDate =:answerDate");
        query.setParameter("answer", forumAns.getAnswer());
        query.setParameter("forumAnswerId", forumAns.getForumAnswerId());
        query.setParameter("farmerUuid", forumAns.getFarmer());
        query.setParameter("answerDate", forumAns.getAnswerDate());
        session.merge(forumAns);
        session.getTransaction().commit();
    } catch (Exception e) {
        e.printStackTrace();
        System.out.println("error while saving forum details" + e);
    } finally {
        session.close();
    }

    return forumAns;
}

Thea

Answer 1

I think you have misplaced @JsonManagedReference and @JsonBackReference.

@JsonManagedReference : its forward part of reference so it will apply on collection type.

@JsonBackReference: its back part of reference.

so your code must be like

  @JsonManagedReference 
     private List<ForumAnswerReplay> forumAnswerReplayList;

 @JsonBackReference
    private ForumAnswer forumAnswer;

you can also use @JsonIdentityInfo you have to apply

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, 
                  property  = "forumAnswerId", 
                  scope     = Long.class)
public class ForumAnswer {
}

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, 
                  property  = "replyId", 
                  scope     = Long.class)
public class ForumAnswerReplay {
}

Smithsonite

thank you for your replay. in properties level instead of @JsonManagedReference i'm using @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "forumAnswerId") but not working.same issue i'm facing. – Thea

@umapati: you have to remove @JsonManagedReference and @JsonBackReference and add @JsonIdentityInfo on both class. – Smithsonite

i removed both annotations and i added @JsonIdentityInfo class level. now data is saving successfully but retrieving time data not reaching to ui. – Thea

you have only posted code for save. update your question and write code you tried for retrieval. – Smithsonite

So @JsonBackReference goes only with @ManyToOne and @JsonManagedReference goes only with @OneToMany ? – Calvo

Answer 2

Remove @JsonManagedReference in ForumAnswer class.

ForumAnswer class:

@Fetch(value = FetchMode.SELECT)
    @OneToMany(cascade = CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinColumn(name = "forumAnswerId")
    private List<ForumAnswerReplay> forumAnswerReplayList;

In ForumAnswerReplay:

@JsonBackReference
public ForumAnswer getForumAnswer() {
    return forumAnswer;
}

Idellaidelle

Answer 3

Use @JsonBackReference for @OneToMany and @JsonManagedReference for @ManyToOne relation to allow Jackson to better handle the relation.

Berliner

What about @ManyToMany? – Lionfish

If you only want to avoid recursion, you can use @JsonIdentityInfo for Parent class. You can see baeldung.com/… for further clarification. Thank you! – Berliner

Everyone links to that one "tutorial" at 'baeldung', but it doesn't really explain anything. – Cistercian

\@JsonBackReference goes on the child, the non-collection \@ManyToOne. fasterxml.github.io/jackson-annotations/javadoc/2.11/com/… \@JsonManagedReference goes on the parent, the\@OneToMany collection – Martinamartindale

Answer 4

I had a similar issue recently, I tried to debug the code, I searched all around the internet and what helped finally was this:

Make sure you set your @JsonBackReference and @JsonManagedReference to have a unique value, for instance in my Department class I have:

    @JsonManagedReference(value = "faculty-department")
    @OneToMany(mappedBy = "department")
    private List<Faculty> faculties;

and in my Faculty class, I have:

    @JsonBackReference(value = "faculty-department")
    @ManyToOne
    private Department department;

When working on a project with just two entities, I noticed that the code was OK, but when the code base grew to more than 5 entities. This error tends to occur if you have multiple relationships with more than one @JsonBackReference in the same entity/class.

If the code builds successfully you may still get a 415 media unsupported error even if you select application/json as your content type while posting, so you will have to set the value as a unique key shared across related entities.

Using SpringBoot 3.1.1 at the time of this answer.

Robena