Springboot Hibernate One to Many infinty recursion

Question

I have two SQL tables as follow:

users
id
username
password
...and more irrelevant stuff

activities
id
name
description
users

I created two entities classes with their Repository (with the anotation @RepositoryRestResource)

@Entity
public class Users {
    @Id
    private int id;
    private String username;
    private String password;

    @OneToMany(mappedBy = "users")
    private Set<Activities> activities;

    public Set<Activities> getActivities() {
        return activities;
    }

//constructors && getters setters

and

@Entity
public class Activities {

    @Id
    private int id;

    @ManyToOne
    @JoinColumn(name = "users")
    private Users users;

    private String name;

    private String description;

//constructors && get

I created an endpoint to test the workflow, by creating an activity. It's all hardcoded as follow

 @RequestMapping("/calendar")
    public Set<Activities> goToCalendar(Authentication authentication){
        Users user = unbreakableService.isAuth(authentication);
        Activities activities = new Activities(user,"karate", "entrenobueno");
        activitiesRespository.save(activities);
        return usersRepository.findByUsername(user.getUsername()).getActivities();
    }

The code is saving the activity correctly, but, when it's supposed to return the list of activities, it returns an infinity recursive information, like:

[{"id":161,"users":{"id":121,"username":"Ojka","password":"$2a$10$Z/bj.5JvQmPquJ67fqF.leUyBkkXJ/2x3z/.bUon8YsIAdV8HMnoG","email":"ojka","pushup":99999,"pullup":null,"handstandhold":9999,"handstandpushup":null,"frontlever":null,"backlever":null,"activities":[{"id":161,"users":{"id":121,"username":"Ojka","password":"$2a$10$Z/bj.5JvQmPquJ67fqF.leUyBkkXJ/2x3z/.bUon8YsIAdV8HMnoG","email":"ojka","pushup":99999,"pullup":null,"handstandhold":9999,"handstandpushup":null,"frontlever":null,"backlever":null,"activities":[{"id":161,"users":{"id":121,"username":"Ojka","password":"$2a$10$Z/bj.5JvQmPquJ67fqF.leUyBkkXJ/2x3z/.bUon8YsIAdV8HMnoG","email":"ojka","pushup":99999,"pullup":null,"handstandhold":9999,"handstandpushup":null,"frontlever":null,"backlever":null,"activities":[{"id":161,"users":{"id":121,"username":"Ojka","password":"$2a$10$Z/bj.5JvQmPquJ67fqF.leUyBkkXJ/2x3z/.bUon8YsIAdV8HMnoG","email":"ojka","pushup":99999,"pullup":null,"handstandhold":9999,"handstandpushup":null,"frontl

I can't read the whole log since the console doesn't show that much information. This is the first error I can see

 Failure while trying to resolve exception [org.springframework.http.converter.HttpMessageNotWritableException]

java.lang.IllegalStateException: Cannot call sendError() after the response has been committed.

And this is the last line of the log

2020-01-25 20:48:54.795 ERROR 19924 --- [nio-8080-exec-2] s.e.ErrorMvcAutoConfiguration$StaticView : Cannot render error page for request [/api/calendar] and exception [Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: com.unbreakable.unbreakable.persistance.Users["activities"]->org.hibernate.collection.internal.PersistentSet[0]->com.unbreakable.unbreakable.persistance.Activities["users"]->com.unbreakable.unbreakable.persistance.Users["activities"]->org.hibernate.collection.internal.Persi....

If I check the table activities (SELECT * FROM ACTIVITIES) there's no infinity information. Just a few activities (the ones I created testing it).

I believe, it should return a Set of activities that the user has.

Answer 1

You can suppress the output in json in a couple of ways:

1. You can use @JsonIgnore over the field with the relationship (activities or users).
2. If you want to generate the json with the parent but not with the children, you can annotate users with @JsonBackReference and activities with @JsonManagedReference