Java Spring boot JPA循环引用

Question

using MySQL, Java, Spring Boot and JPA

I have two objects, user and module.

A user can have many modules and a module can have many users.

A module is structured the following way:

@Entity
@Table(name = "module")
public class Module {
    @Id
    @GeneratedValue( strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @ManyToMany
    @JoinTable(name="module_users",
       joinColumns = @JoinColumn(name="module_id"),
       inverseJoinColumns =  @JoinColumn(name = "user_id")
    )
    private Set<User> users = new HashSet<>();

A user is structured the following way:

@Entity
@Table(name = "user")
public class User implements Serializable {
    @Id
    @GeneratedValue( strategy = GenerationType.IDENTITY) 
    public Long id;
    public String name;
    private String email;
    @JsonIgnore
    @ManyToMany(mappedBy = "users")
    public Set<Module> modules = new HashSet<>();

Having @JsonIgnore annotation does "work" when calling modules, but I also need to call a user and its modules ideally. Any suggestions to support both of these without crashing from circular referencing?

Answer 1

在这种情况下你可以使用 DTO 检查这里

Answer 2

Use these two annotations @JsonManagedReference and @JsonBackReference

Ref: http://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion

@Entity
@Table(name = "module")
public class Module {
    @Id
    @GeneratedValue( strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @ManyToMany
    @JoinTable(name="module_users",
       joinColumns = @JoinColumn(name="module_id"),
       inverseJoinColumns =  @JoinColumn(name = "user_id")
    )
    @JsonBackReference
    private Set<User> users = new HashSet<>();

A user is structured the following way:

@Entity
@Table(name = "user")
public class User implements Serializable {
    @Id
    @GeneratedValue( strategy = GenerationType.IDENTITY) 
    public Long id;
    public String name;
    private String email;
    @JsonManagedReference
    @ManyToMany(mappedBy = "users")
    public Set<Module> modules = new HashSet<>();