JsonManagedReference 与 JsonBackReference

Question

我想知道杰克逊@JsonManagedReference和@JsonBackReference的区别？

Answer 1

@JsonManagedReference is the forward part of reference – the one that gets serialized normally. @JsonBackReference is the back part of reference – it will be omitted from serialization.

所以他们真的取决于你们关系的发展方向

public class User {
    public int id;
    public String name;

    @JsonBackReference
    public List<Item> userItems; 
} 

public class Item {
    public int id;
    public String itemName;

    @JsonManagedReference
    public User owner; 
 }

Answer 2

@JsonManagedReference 和 @JsonBackReference 旨在处理字段之间的这种双向链接，一个用于父角色，另一个用于子角色。

For avoiding the problem, linkage is handled such that the property annotated with @JsonManagedReference annotation is handled normally (serialized normally, no special handling for deserialization) and the property annotated with @JsonBackReference annotation is not serialized; and during deserialization, its value is set to instance that has the "managed" (forward) link.

Answer 3

@JsonManagedReference -> 管理引用的前向部分，此注释标记的字段是被序列化的字段
@JsonBackReference -> 管理引用的反向部分，标有此注解的fields/collections不序列化。

用例： 您的 entities/tables 中有一对多或多对多关系，不使用上述关系会导致

之类的错误

Infinite Recursion and hence Whosebug - > Could not write content: Infinite recursion (WhosebugError)

出现上述错误是因为 Jackson（或其他类似的人）试图序列化关系的两端并以递归结束。

@JsonIgnore 执行类似的功能，但上面提到的注释更可取。

Answer 4

我比较喜欢
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Long.class)
其中属性是主键字段的名称，范围是它的类型

Answer 5

正如 Rajat Verma 所写，他的解决方案非常有效。谢谢你为我节省了很多时间和愤怒:-)

The important Part:
You need define fields as List, I had that as Set before and this solution NOT WORKING (appears as infinite loop)!

我添加我的解决方案：

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Long.class)
public class Agent {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToMany(mappedBy = "subscribers")
    @ApiModelProperty(dataType = "List", example = "[1,2,3]") // for Swagger
    @JsonIdentityReference(alwaysAsId = true) // show only id of Topic
    private final List<Topic> subscribeTopics = new ArrayList<>()
}

 @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = Long.class)
 public class Topic {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToMany(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
    @JoinTable(name = "topic_agent",
        joinColumns = @JoinColumn(name = "fk_topic_id"),
        inverseJoinColumns = @JoinColumn(name = "fk_agent_id"))
    @ApiModelProperty(dataType = "List", example = "[1,2,3]")
    @JsonIdentityReference(alwaysAsId = true)
    private final List<Agent> subscribers = new ArrayList<>();
 }

JsonManagedReference 与 JsonBackReference

JsonManagedReference vs JsonBackReference

java

jackson