Json : generate object id instead of real object - json

Question

On my server I have complex objects but in my web client I would like to get a simple representation of these objects.
I would like to replace object with their id for example:
#JsonAutoDetect
public class Event{
private Long id;
private String name;
private User user;
#JsonProperty("event_id")
public Long getId() {
return event_id;
}
public String getName() {
return name;
}
public String getUser() {
return user;
}
....setters
}
When generating Json I will get Event class and user class inside
Is there anyway to replace the User with user id?
Since I have many complex objects I am looking for an elegant way like maybe an annotation over the User object that will return only the object id.
Ofcourse I will need the other way around. getting the id and transforming it to the object.
BTW: I'm using Jackson
Any Ideas?
10x
Noam

Answer 1

You can expose a property for Id and ignore the sub-entity property like this:
class Event {
private User user;
public Long getUserId() {
return user.getId();
}
public void setUserId(Long userId) {
this.user = retrieveUserById(userId); // or any other code
}
#JsonIgnore
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}

Answer 2

Here is my idea how to achieve it. You can use #JsonRawValue(true) annotation on your user property. This will make Jackson treat user object as already serialized stuff. And then just override .toString() method for User class to make it return it's id as a string.
So in your Event class:
public class Event {
...
#JsonRawValue(true)
private User user;
...
}
And in your User class:
public class User {
...
private Integer id;
...
#Override
public String toString() {
return id.toString();
}
...
}
This will result in e.g. "user": 5 in your json (no double quotes will be added around User object serizlized value).