无法写入 JSON：未能一对一延迟初始化角色集合

Question

I have the following code... It's an application where the user has a wall, and on that wall there can be several games.

@Entity
@Table(name = "tb_user")
public class User implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @OneToOne(mappedBy = "user",fetch = FetchType.EAGER)
    private Mural mural;

    public User() {

    }

    public User(Long id, String name, Mural mural) {
        this.id = id;
        this.name = name;
        this.mural = mural;

     //getters and setters...
    }

@Entity
@Table(name = "tb_mural")
public class Mural implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @ManyToMany
    @JoinTable(name = "tb_mural_games",
            joinColumns = @JoinColumn(name = "mural_id"),
            inverseJoinColumns = @JoinColumn(name = "games_id"))
    private Set<Game> games = new HashSet<>();

    @OneToOne
    @JoinColumn(name = "user_id")
    private User user;

    public Mural() {

    }

    public Mural(Long id, String name, User user) {
        this.id = id;
        this.name = name;
        this.user = user;
    }
 
    //getters and setters...

And the following request...

 @GetMapping
    public ResponseEntity<List<User>> findAll(){
        List<User> list = repository.findAll();
        return ResponseEntity.ok().body(list);
    }

But I have the following error...

 Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role... continue...

I tried using FETCH.EAGER but it doesn't work, it only works if I use jsonignore, but I would like it to return the "mural" in the user request.

Answer 1

Put the JsonIgnore in the Mural class on

@OneToOne
@JoinColumn(name = "user_id")
private User user;

Also try to avoid directly returning entities to the end user. Either try to map the entity to DTO or use projection ( https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections ).