Spring boot - no back reference property found from type[]

Question

I have 2 entities in spring: Category and Position with a OneToMany relation:

Category.java:

@Table(name = "category")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    int id;

    int parentId;
    String name;

    @OneToMany(mappedBy = "category")
        @JsonManagedReference(value = "referenceCallInCategory")
    List<Position> positionList;

// getters and setters

Position.java:

@Entity
public class Position {

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

    String position;
    String company;
    String description;

    @ManyToOne
//        @JsonBackReference (value = "referenceCallInPosition")
    @JsonIgnoreProperties({"parentId","name","positionList"})
    Category category;

// getters and setters

When I make a post request for a position through postman I get the following warning in my terminal: WARN 15904 --- [nio-8080-exec-2] .c.j.MappingJackson2HttpMessageConverter : Failed to evaluate Jackson deserialization for type [[simple type, class positionsSite.positions.mode l.Position]]: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot handle managed/back reference 'referenceCallInCategory': no back reference property found from type [collection type; class java.util.List, contains [simple type, class positionsSite.positions.model.Position]]

The strange thing is when making a postrequest for a category the exact same warning occurs but after I make a postrequest for category, the postrequests for position work without a problem. Until I restart the application, then it fails again.

The reason I have @JsonIgnoreProperties instead of @JsonBackReference is that I need the Category.id when I make a get request for position. Given the warning no back reference property found I tried the @JsonBackReference as commented in the code, but this did not change anything.

Any help on how to solve this would be much appreciated

Unrelated to the question, but have you been considering why you have setters for (if you have) private variables? If you can both get and set a private variable should it be private? — darclander, Sep 08 '20 at 10:59
Also, does [this](https://stackoverflow.com/questions/37392733/difference-between-jsonignore-and-jsonbackreference-jsonmanagedreference) post help you or are you familiar with how the different `@Json` works? — darclander, Sep 08 '20 at 11:05
@darclander it was quit some time since I last worked with the different ```@Json``` properties. I thought I still knew them well enough but the post you mentioned worked wonders for my memory, so thanks :). The ```@JsonManagedReference``` is unnecessary if I use the ```@JsonIgnoreProperties```. — EBolt, Sep 08 '20 at 11:27
@darclander regarding the getters and setters: you are right to mention this. It is more of a convenience issue while developing. It's not the most neat way of working but some habit of mine to create all getters and setters first and delete the ones I do/should not use together with a larger safety check — EBolt, Sep 08 '20 at 11:31
Take a look at similar questions: [Jackson serialize problem in @ManyToMany relationship](https://stackoverflow.com/questions/61392551/jackson-serialize-problem-in-manytomany-relationship/61398920#61398920), [Jackson/Hibernate, meta get methods and serialization](https://stackoverflow.com/questions/55383889/jackson-hibernate-meta-get-methods-and-serialization/55386877#55386877). — Michał Ziober, Sep 08 '20 at 13:11

score 0 · Accepted Answer · answered Sep 08 '20 at 11:33

0

As mentioned by @darclander, this post shows clear explanation of the different @Json properties. My mistake was that I still had a @JsonManagedReference which gave the problem. I deleted it and not everything works perfect.

answered Sep 08 '20 at 11:33

EBolt

11
2

It's great to hear my comment helped! If you want to you can set this as the answer to help people with similar problems in the future :). – darclander Sep 08 '20 at 14:21

Spring boot - no back reference property found from type[]

1 Answers1