Spring boot JPA - JSON without nested object with OneToMany relation

Question

I have a project which deals with some ORM mapping of objects (there are some @OneToMany relations etc).

I am using REST interface to treat these objects and Spring JPA to manage them in the API.

This is an example of one of my POJOs:

@Entity
public class Flight {
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 private long id;
 private String name;
 private String dateOfDeparture;
 private double distance;
 private double price;
 private int seats;
 @ManyToOne(fetch = FetchType.EAGER)
 private Destination fromDestination;
 @ManyToOne(fetch = FetchType.EAGER)
 private Destination toDestination;
 @OneToMany(fetch = FetchType.EAGER, mappedBy = "flight")
 private List<Reservation> reservations;
}

When making a request, I have to specify everything in the JSON:

{
 "id": 0,
 "reservations": [
 {}
 ],
 "name": "string",
 "dateOfDeparture": "string",
 "distance": 0,
 "price": 0,
 "seats": 0,
 "from": {
 "id": 0,
 "name": "string"
 },
 "to": {
 "id": 0,
 "name": "string"
 }
}

What I would prefer, is actually specifying the id of referenced object instead of their whole bodies, like this:

{
 "id": 0,
 "reservations": [
 {}
 ],
 "name": "string",
 "dateOfDeparture": "string",
 "distance": 0,
 "price": 0,
 "seats": 0,
 "from": 1,
 "to": 2
}

Is that even possible? Could someone give me some insight on how to do this? I am only finding tutorials on how to do the opposite (the solution I already have).

• VadymVL: You can try find this useful - wiki.fasterxml.com/JacksonFeatureObjectIdentity

Answer 1

Yes, it is possible.

For this purpose you should use pair of Jackson annotations to your entity model:

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIdentityReference(alwaysAsId = true)
protected Location from; 

Your serialized JSON will look instead of this:

{
 "from": {
 "id": 3,
 "description": "New-York"
 } 
}

like this:

{
 "from": 3
}

As mentioned in official documentation:

@JsonIdentityReference - optional annotation that can be used for customizing details of a reference to Objects for which "Object Identity" is enabled (see JsonIdentityInfo)

alwaysAsId = true used as marker to indicate whether all referenced values are to be serialized as ids (true);

Note that if value of 'true' is used, deserialization may require additional contextual information, and possibly using a custom id resolver - the default handling may not be sufficient.

• kiedysktos: is @JsonIdentityInfo necessary here?

Answer 2

You can only ignore your JSON content using @JsonIgnore annotation. The field which you want to hide in your JSON at there you can annotate that with @JsonIgnore. You can change your JSON like this :

{
 "id": 0,
 "reservations": [
 {}
 ],
 "name": "string",
 "dateOfDeparture": "string",
 "distance": 0,
 "price": 0,
 "seats": 0,
 "from": {
 "id": 0
 },
 "to": {
 "id": 0
 }
}

But You can't like this:

{
 "id": 0,
 "reservations": [
 {}
 ],
 "name": "string",
 "dateOfDeparture": "string",
 "distance": 0,
 "price": 0,
 "seats": 0,
 "from": 0,
 "to": 1
}

• PhoneixS: I think the second part isn't true as show by the other answer.
• Johan: I agree with @Amit khanduri
• nayan dhabarde: This does not work if one request needs the nested data and other doesnt. Let's say I have a shop and an item. I want an item name of which I have and I want to retreive it with couple of shop details. Do you know a way to do that in spring boot?