@Target(value=FIELD)
@Retention(value=RUNTIME)
public @interface ObjectId
Created by Xiaofei on 16/3/25.
Indicates the object id of an object.
The data storage stores the objects according to their class id and object id.
If an object has a field of the String type annotated by the ObjectId annotation, the value of
the field is used as the object id of the object.
If an object do not have such an annotated field or the annotated filed is not of the String type,
a specified id should be provided when the data storage stores the object.
Distinct objects of the same class should have distinct object ids. If not, the behavior is unspecified.