Springboot Hibernate 一对多无限递归

Question

我有两个 SQL 表如下：

用户
ID
用户名
密码
...以及更多不相关的东西

活动
ID
名称
描述
用户

我用它们的存储库创建了两个实体类（带有注释@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

和

@Entity
public class Activities {

    @Id
    private int id;

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

    private String name;

    private String description;

//constructors && get

我通过创建活动创建了一个端点来测试工作流程。全部硬编码如下

 @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();
    }

该代码正确保存了活动，但是，当它应该返回活动列表时，它会返回无限递归信息，例如：

[{"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

我无法阅读整个日志，因为控制台没有显示那么多信息。这是我看到的第一个错误

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

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

这是日志的最后一行

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....

如果我检查表活动（SELECT * FROM ACTIVITIES），则没有无限信息。只是一些活动（我创建的测试它的活动）。

我相信，它应该返回用户拥有的一组活动。

Answer 1

您可以通过多种方式抑制 json 中的输出：

1. 您可以通过关系 (或)@JsonIgnore在字段上使用。activitiesusers
2. 如果你想与父级一起生成json而不是与子级一起生成json，则可以使用users和@JsonBackReference进行activities注释@JsonManagedReference