Jackson with Spring MVC duplicate nested objects not deserializing

Question

I am trying to Convert following POJO to a JSON in `@RestController`: ``` @Entity @Table(name="user_location") @NamedQuery(name="UserLocation.findAll", query="SELECT u FROM UserLocation u") public class UserLocation implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private int id; private String addr1; private String addr2; private String landmark; private BigDecimal lat; private BigDecimal lng; private String zipcode; //bi-directional many-to-one association to City @ManyToOne private City city; //bi-directional many-to-one association to State @ManyToOne private State state; public UserLocation() { } //Getter - Setters } ``` Nested City.java is as follow: ``` @Entity @NamedQuery(name="City.findAll", query="SELECT c FROM City c") @JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, property="@id", scope = City.class) public class City implements Serializable { private static final l…

Accepted Answer

This is how jackson designed JsonIdentityInfo annotation logic.

```
 * Annotation used for indicating that values of annotated type
 * or property should be serializing so that instances either
 * contain additional object identifier (in addition actual object
 * properties), or as a reference that consists of an object id
 * that refers to a full serialization. In practice this is done
 * by serializing the first instance as full object and object
 * identity, and other references to the object as reference values.
```

Jackson will run the full serialization first time and only id will be serialized when it find that object second time.

So, there is two ways how you can fix it:

1) you can simple remove the @JsonIdentityInfo annotation and Jackson will serialize object as you expected but it will remove the @id field from the response. This is probably fine because you still will have 'id' property.

2) I feel like you can simply restructure your objects and delete some references. I would say it is good to do these changes anyway. First of all you can delete reference to the State from UserLocation. I would say that it is not necessary to have the State in userLocation class because of the State is attached to the City. By doing this you will access State from the City and your problem is solved. Also I would delete the reference to the list of userLocations from the City class as well as from State class.

It will look like:

UserLocation has City and doesn't have State.

City has State and doesn't have userLocations

State doesn't have userLocations as well as cities.

Hope this helps

Jackson with Spring MVC duplicate nested objects not deserializing

Solution

Problem