Jackson circular dependencies on deserialization with @JsonIdentityInfo

Recently I had to implement a RESTful service which had to have a CRUD interface for storing entities with circular dependencies given as JSON. Usually if you have for example an object like this:

"graph": {
          "nodes": [{"name":"n1"}, {"name":"n2"}],
          "transitions": [{"source": {"name":"n1"}, "target": {"name":"n2"}]
}

and having these Java classes:

@Entity
class Graph {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    long id = 0;

    List<Node> nodes = new ArrayList<Node>();
    
    List<Transition> transitions = new ArrayList<Transition>();
}

@Entity
class Node {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    long id = 0;

    String name = "";
}

@Entity
class Transition {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    long id = 0;

    Node source;

    Node target;
}

the nodes would be deserialized into 4 Java objects and therefore storing with different ids in the database. If you want instead referencing inside the JSON string the already defined nodes you have to add the @JsonIdentityInfo above the entities.

@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
@Entity
class Node {
     @Id
     @GeneratedValue(strategy=GenerationType.AUTO)
     long id = 0;

     String name = "";
}

After that you can define your references by using the id you used for nodes and the transitions will have references to the correct nodes.

"graph": {
          "nodes": [{"@id":"1", "name":"n1"}, {"@id":"2", "name":"n2"}],
          "transitions": [{"source": "1", "target": "2"]
}