在Hibernate / Spring数据中从双向一对多关系获取数据

Question

As following the instructions or tutorials posted online on how to create a bidirectional One To Many relationships in Hibernate, I was able to create two entity classes:

@Entity
@Table(name = "user")
public class User {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;

@Column(name = "user_name",nullable = false)
private String userName;

@Column(name="password",nullable = false)
private String password;

@OneToMany (mappedBy = "user",cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Set<BlogPost> blogPostSet;

//getters and setters

}

@Entity
@Table(name = "blog_post")
public class BlogPost {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;

@Column(nullable = false)
private String title;

@Column(nullable = false)
private String content;

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

//getters and setters
}

I was able to insert data on these two entities, but the problem occurs when I try to fetch data a recursion happens and results to a stackoverflow error, please see the attached screenshot. What would be the proper way to fetch data on this hibernate relationship?

Answer 1

Mapping seems to be fine, probably you have overridden toString() method in both of the entities printing each others relationship references like

class Employee{
public String toString(){
    return "blogPostSet "+blogPostSet;
}
class BlogPost{
public String toString(){
    return "employee "+employee;
}

Hence calling each others toString() to cause a stackoverflow error.

Answer 2

You have to change your toString() method, of both classes so that it doesn't get recursive. By changing that you can yourself print the things you want so that it doesn't go into recursion.

Answer 3

由于两个实体的ID均为字段名称，因此您必须指定@JsonIdentityInfo（generator = ObjectIdGenerators.PropertyGenerator.class，property =“ id”），它将解决此问题。