java - @jsonbackreference 不绑定(bind)关系

Question

我有两个类:

人.java:

@Entity
@PrimaryKeyJoinColumn(name="owner_id")
public class Person extends Owner {

    @ManyToOne
    @JoinColumn(name = "car_sharing_id")
    @JsonBackReference
    private CarSharing carSharing;
}

汽车共享.java:

@Entity
public class CarSharing extends MetadataEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToOne
    @JoinColumn(name = "owner_id", nullable = false)
    @NotNull
    private Person owner;

    @OneToMany(mappedBy = "carSharing", cascade = CascadeType.ALL)
    @Valid
    private Set<Person> members;
}

我正在使用 @JsonBackReference 来避免无限循环。 CarSharing 类工作正常，问题只发生在 Person 类。

获取人员似乎忽略了 carSharing 属性。由于它在返回到服务器时为 null，因此更新取消了对 person 表中 carsharing_id 的引用的链接。

停止循环很好，但我还需要 Person 类中可用的 carSharing。

知道如何解决这个问题吗？

Answer 1

如果您使用的是 Jackson 2.x，则可以使用注解 @JsonIdentityInfo:

Whether Object Identity information is to be used for determining how to serialize/deserialize property value to/from JSON (and other data formats) will be based on existence (or lack thereof) of @JsonIdentityInfo annotation.
see: http://wiki.fasterxml.com/JacksonFeatureObjectIdentity

例如，如果您注释类 CarSharing:

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;
//...
@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
public class CarSharing {

一个人(我给这个类加了字段名)的JSON结果是:

  {
    "carSharing": {
      "@id": 1,
      "id": 12345,
      "owner": {
        "carSharing": 1,
        "name": "owner"
      },
      "members": [
        {
          "carSharing": 1,
          "name": "owner"
        },
        {
          "carSharing": 1,
          "name": "driver2"
        },
        {
          "carSharing": 1,
          "name": "driver"
        }
      ]
    },
    "name": "driver2"
  }

还有一个带有 id=12345 的 CarSharing 实例:

  {
    "@id": 1,
    "id": 12345,
    "owner": {
      "carSharing": 1,
      "name": "owner"
    },
    "members": [
      {
        "carSharing": 1,
        "name": "owner"
      },
      {
        "carSharing": 1,
        "name": "driver2"
      },
      {
        "carSharing": 1,
        "name": "driver"
      }
    ]
  }

字段 @id 是从 jackson 生成的。如果引用对象未序列化，则该值设置为引用对象的@id。