Deserializing from JSON using foreign key

Question

I have a many to one relationship: A *<-->1 B and I want to deserialize A from a JSON having B 's primary key ( B exists in db with that primary key):

{
    "b": 1
}

I have tried the following:

@Entity
@Table(name = "table_a")
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class A implements Serializable {

    @JsonIgnore
    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "b", unique = true, nullable = false)
    private B b;
}

and

@Entity
@Table(name = "table_b")
public class B implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @OneToMany(mappedBy = "b")
    private List<A> a = new ArrayList<>();
}

but object A is created with b = null . How can I deserialize A with b property correctly instantiated from db?

Note: I am using Jackson version 2.6.1.

Answer 1

You have several options and here is similar question :

1. @JsonCreator factory in B class ( More info )

2. Custom deserializer

3. Custom ObjectIdResolver for @JsonIdentityInfo like

   private class MyObjectIdResolver implements ObjectIdResolver { private Map<ObjectIdGenerator.IdKey,Object> _items = new HashMap<>(); @Override public void bindItem(ObjectIdGenerator.IdKey id, Object pojo) { if (!_items.containsKey(id)) _items.put(id, pojo); } @Override public Object resolveId(ObjectIdGenerator.IdKey id) { Object object = _items.get(id); return object == null ? getById(id) : object; } protected Object getById(ObjectIdGenerator.IdKey id){ Object object = null; try { //can resolve object from db here //objectRepository.getById((Integer)idKey.key, idKey.scope) object = id.scope.getConstructor().newInstance(); id.scope.getMethod("setId", int.class).invoke(object, id.key); } catch (Exception e) { e.printStackTrace(); } return object; } @Override public ObjectIdResolver newForDeserialization(Object context) { return new MyObjectIdResolver(); } @Override public boolean canUseFor(ObjectIdResolver resolverType) { return resolverType.getClass() == getClass(); } }

   And use it like this:

    @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, resolver = MyObjectIdResolver.class, property = "id", scope = B.class) public class B { // ... }

Here is your case relatedgist demo more broad github project with some serialization thoughts