如何避免 Spring 中一对一关系的无限循环？

Question

In my application we are having some trouble dealing with people with spouse, the problem is that each person may have a spouse, and this spouse will have to have this person. If you think close about it you will notice that this relation creates a infinite loop.

Normally I would resolve this by putting a @JsonIgnore at the "spouse" attribute, but I we use this attribute in our requests because we use Json's to create the object.

I would try to use @JsonManagedReference and @JsonBackReference , but there's just one class, the class "person", the loop is happening because this class has itself.

Is there other annotation that I'm forgetting? or other way to fix this?

Answer 1

You need to use @JsonIdentityInfo annotation:

@Getter
@Setter
@AllArgsConstructor
@ToString
@JsonIdentityInfo(generator= ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
public class Person {
    private final String name;
    private final int age;
    private final String address;

    private Person spouse;
    
    public boolean isMarried() {
        return null != spouse;
    }
}

// test
ObjectMapper mapper = new ObjectMapper();

Person john = new Person("john", 28, "London", null);
Person gill = new Person("gill", 24, "London", null);
john.setSpouse(gill);
gill.setSpouse(john);
        System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(john));       

Output printed:

{
  "@id" : 1,
  "name" : "john",
  "age" : 28,
  "address" : "London",
  "spouse" : {
    "@id" : 2,
    "name" : "gill",
    "age" : 24,
    "address" : "London",
    "spouse" : 1,
    "married" : true
  },
  "married" : true
}

If you have property id defined inside your class, you should use @JsonIdentityInfo(generator= ObjectIdGenerators.PropertyGenerator.class, property="id") .