java - Serialize bi-directional JPA entities to JSON with jackson

Question

I'm using Jackson to serialize my JPA model into JSON.

I have the following classes:

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
}

and

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
}

I'm using the POJO mapping to serialize from model to JSON. When I serialize a Parent object I get the following JSON:

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

But when I serialize a Child I get the following JSON:

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

The reference to the parent is missing. Is there a way to solve this?

Answer 1

I think you have to choose between the @JsonIdentityInfo and the @JsonBackReference / @JsonManagedReference.

I would go with : @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property="id") on your entities, removes @JsonBackReference / @JsonManagedReference pairs.

And add @JsonIgnore on the fields you want to exclude.