反序列化外键

Question

我有一个多对一的关系：A * < - >图1B和欲反序列化从具有乙的主键（乙一个JSON甲存在于分贝与该主键）：

{ 
    "b": 1 
} 

我曾尝试以下：

@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; 
} 

和

@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<>(); 
} 

但对象甲与b = null创建。我如何反序列化A与b属性正确实例化从数据库？

注意：我正在使用杰克逊版本2.6.1。

Answer 1

您有几种选择，这里是similar question：

1. @JsonCreator厂B类（More info）

2. 自定义解串器

3. 定制ObjectIdResolver为@JsonIdentityInfo像

   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(); 
       } 
   } 
   

   而且使用这样的：

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

这里是你的情况下，相关gist demo更加广阔github project有些系列化的想法