使用jackson将双向JPA实体序列化为JSON

Question

我正在使用Jackson将我的JPA模型序列化为JSON.

我有以下课程:

import com.fasterxml.jackson.annotation.*;
import javax.persistence.*;
import java.util.Set;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class)
@Entity
public class Parent {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String name;

  @JsonManagedReference
  @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
  private Set<Child> children;

  //Getters and setters
}

和

import com.fasterxml.jackson.annotation.*;
import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class)
@Entity
public class Child {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String name;

  @JsonBackReference
  @ManyToOne
  @JoinColumn(name = "parentId")
  private Parent parent;

  //Getters and setters
}

我正在使用POJO映射从模型序列化为JSON.当我序列化一个Parent对象时,我得到以下JSON:

{
  "id": 1,
  "name": "John Doe",
  "children": [
    {
      "id": 1,
      "name": "child1"
    },{
      "id": 2,
      "name": "child2"
    }
  ]
}

但是当我序列化一个Child时,我得到以下JSON:

{
  "id": 1,
  "name": "child1"
}

缺少对父项的引用.有办法解决这个问题吗？

Answer 1

我认为你必须在@JsonIdentityInfo和@JsonBackReference/@JsonManagedReference之间进行选择.

我会在你的实体上使用:@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class,property ="id"),删除@JsonBackReference/@JsonManagedReference对.

并在要排除的字段上添加@JsonIgnore.

Answer 2

您可以使用JsonManagedReference/JsonBackReference,同时使用JsonIdentityInfo来补充双向关系.

问题类:

// bi-directional one-to-many association to Answer (Question is owner)
@JsonManagedReference
@OneToMany(mappedBy = "question", cascade = CascadeType.ALL)
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, property = "@QuestionAnswers")
private Set<Answer> answers = new HashSet<>();

在回答Class://与问题的双向多对一关联

@JsonBackReference
@ManyToOne
@JoinColumn(name = "questionId", referencedColumnName="id", foreignKey = @ForeignKey(name = "fk_answer_question"))
private Question question;

如果您需要在子对象中使用父引用,请删除托管/后退引用,这对我来说很好.