spring-data-jpa多对多双向映射，查询进入死循环

Question

两个实体类

User

@Data
@Entity
@Table(name = "sys_user")
public class User {
    @Id
    @GeneratedValue
    @Column(name = "user_id")
    private Integer userId;
    @Column(name = "username")
    private String username;
    @ManyToMany(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY)
    @JoinTable(
            name = "user_role",
            joinColumns = {@JoinColumn(name = "user_id")},
            inverseJoinColumns = {@JoinColumn(name = "role_id")}
    )
    private Set<Role> roles;
}

Role

@Data
@Entity
@Table(name = "sys_role")
public class Role {
    @Id
    @Column(name = "role_id")
    private Integer roleId;
    @Column(name = "role_name", unique = true)
    private String roleName;
    @ManyToMany(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY, mappedBy = "roles")
    private Set<User> users;

测试代码

    @Transactional
    @Test
    public void save() throws Exception{
        Set<Role>roles = new HashSet<Role>();
        roles.add(new Role(1, "USER"));
        roles.add(new Role(2, "ADMIN"));

        repository.save(new User("张三", roles));
    }

    @Transactional
    @Test
    public void findAll(){
        List<User> users = repository.findAll();
        for (User user : users) {
            System.out.println(user);
        }
    }

在使用插入数据的时候没有任何问题，但是当查询的时候报错

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: wang.xiaoqiang.manytomany.entity.User.roles, could not initialize proxy - no Session

这个可以理解，懒加载的时候丢失了session无法获取roles信息，当将user中的集合设置为急加载模式fetch = FetchType.LAZY，结果就遇到StackOverflowError。

哪位大佬有相关经历，帮帮忙。。。

Answer 1

之前用JUnit进行单元测试的时候遇到过类似的问题

可以尝试在单元测试类上添加@TestExecutionListeners注解，并传入一个数组，数组中包含TransactionalTestExecutionListener.class

Answer 2

User类里加上@JsonIgnoreProperties(value = { "users" })，Role类里加上@JsonIgnoreProperties(value = { "roles" })，在循环的时候过滤某个字段，在自己的实体里过滤自己，就不会查到第二遍了