How to get rid of cyclic redundancy while having @ManyToMany relation JPA springboot

问题

I am a newbie to the Spring boot (but worked in Laravel). I am facing a problem of cyclic redundancy in @ManyToMany relation. Let's go through the scenario -

What response I ma getting (fetching user's list which has many to many relationships with roles) -

Following is the ER-diagram of associated tables to manage many to many relationship between users and roles table.

User entity class has following code -

@Entity
@Where(clause = "deleted_at IS NULL")
@SQLDelete(sql = "UPDATE users SET deleted_at = CURRENT_TIMESTAMP WHERE id = ?", check = ResultCheckStyle.COUNT)
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "users")
@JsonIgnoreProperties(
        value = {"createdAt", "updatedAt", "deletedAt"}
)
public class User {

    @Id
    @Column(name = "id", updatable = false, nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Column(name = "name", nullable = false)
    @NotBlank(message = "Name field can not be empty")
    private String name;

    .....
    .....
    .....


    @ManyToMany(targetEntity = Role.class, fetch = FetchType.EAGER)
    @JoinTable(name = "user_roles",joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles;

}

And Role entity is as follows -

@Entity
@Table(name = "roles")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@SQLDelete(sql = "UPDATE roles SET deleted_at = CURRENT_TIMESTAMP WHERE id = ?", check = ResultCheckStyle.COUNT)
@Where(clause = "deleted_at IS NULL")
@JsonIgnoreProperties(
        value = {"createdAt", "updatedAt", "deletedAt"}
)
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", updatable = false, nullable = false)
    private long id;

    @Column(name = "title")
    @NotBlank(message = "Title field must be not null")
    private String title;

    ......
    ......
    ......

    @OneToMany(targetEntity = User.class, fetch = FetchType.EAGER)
    @JoinTable(name = "user_roles",joinColumns = @JoinColumn(name = "role_id"),
            inverseJoinColumns = @JoinColumn(name = "user_id"))
    private List<User> users;

}

How to solve this problem? What I am doing wrong here?

回答1:

Since you are fetching the list directly. You will have to mention the annotation @JsonIgnore everywhere you have mapping specified. By everywhere I don't mean literally everywhere. Just use the annotation and see how it works.

Edit -> Just do it in roles table where you have mapped it to the user table. It will then skip the user mapping while fetching the data.

@JsonIgnore
 private List<User> users;

回答2:

Easiest would probably be to annotate the List<T>'s with a @JsonIgnoreProperties annotation to break the cyclic dependencies.

@JsonIgnoreProperties("users")
private List<Role> roles;


@JsonIgnoreProperties("roles")
private List<User> users;

回答3:

You could annotate users within Role with @JsonBackReference.

来源：https://stackoverflow.com/questions/60151132/how-to-get-rid-of-cyclic-redundancy-while-having-manytomany-relation-jpa-spring

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