How to get relationship data with spring boot rest api? - json

Question

I'm building a REST API with Spring Boot to retrieve boat information. I'm using Spring Data Rest and Spring Data JPA. When I get the data from the API, I don't know why the relationship data are not with the others informations.
Do I have to configure something in Spring to get the relationship with my data ?
Here is my file.
Boat entity:
#Entity
#Table(name="boat")
#Data
public class Boat {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#Column(name = "name")
private String name;
#Column(name = "description")
private String description;
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "type_id", nullable = false)
#JsonBackReference
private BoatType type;
}
Boat type entity :
#Entity
#Table(name = "boat_type")
#Data
public class BoatType {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#Column(name = "name")
private String name;
#OneToMany(cascade = CascadeType.ALL, mappedBy = "type")
#JsonManagedReference
private Set<Boat> boats;
}
Boat repository :
#CrossOrigin("http://localhost:4200")
public interface BoatRepository extends JpaRepository<Boat, Long> {
}
JSON response :
{
"_embedded": {
"boats": [
{
"id": 1,
"name": "Boat 1",
"description": "A brief description of the boat 1",
"_links": {
"self": {
"href": "http://localhost:8080/api/boats/1"
},
"boat": {
"href": "http://localhost:8080/api/boats/1"
},
"type": {
"href": "http://localhost:8080/api/boats/1/type"
}
}
},
...
]
}
Result expected (with the type object too) :
{
"_embedded": {
"boats": [
{
"id": 1,
"name": "Boat 1",
"description": "A brief description of the boat 1",
"type": {
"id": 1,
"name": "Motorboats"
},
"_links": {
"self": {
"href": "http://localhost:8080/api/boats/1"
},
"boat": {
"href": "http://localhost:8080/api/boats/1"
},
"type": {
"href": "http://localhost:8080/api/boats/1/type"
}
}
},
...
]
}
I think that the problem is related with Spring Data Rest because when i do the same app with my own controller and repository, i get the data I need.
Is there a way to "configure" spring data rest?

Answer 1

It seems like you've used #JsonBackReference and #JsonManagedReference the other way around, than you needed. You've put #JsonBackReference on the type field in your Boat class, whereas its documentation states:
[...] Linkage is handled such that the property annotated with this annotation is not serialized
So it seems like you need to put #JsonManagedReference annotation on it instead (see: JsonManagedReference documentation) and put #JsonBackReference on boats in your BoatType class.
Alternatively, you could consider using #JsonIdentityInfo instead. See: the documentation.
Also, this article might be helpful. It explains various ways to handle bidirectional relationships using Jackson.

Answer 2

Change #JsonManagedReference and #JsonBackReference to #JsonIgnoreProperties.
In your case:
#OneToMany(cascade = CascadeType.ALL, mappedBy = "type")
#JsonIgnoreProperties(value = {"type"})
private Set<Boat> boats;
and
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "type_id", nullable = false)
#JsonIgnoreProperties(value = {"boats"})
private BoatType type;
You will avoid the infinity loop in json result and get all reference objects (relationships).

Answer 3

The Boat response includes a uri to your BoatType resource by default since you defined a rest repository for your BoatType resource (docs)
To override this behaviour, define a projection to expose the boat type data (docs):
#Projection(name = "boatDetail", types = { Boat.class })
interface BoatDetail {
// ... all other fields you want included in the response
BoatType getType();
}
Then include the projection as a query parameter:
{apiUrl}boats/1?projection=boatDetail
The response should now include the boat type data:
{
"id": 1,
"name": "Boat 1",
"description": "A brief description of the boat 1",
"type": {
"id": 1,
"name": "Motorboats"
},
"_links": {
// ...
}
}
To automatically include the projection on a collection of resources, use an excerpt (docs):
#RepositoryRestResource(excerptProjection = BoatDetail.class)
interface BoatRepository extends JpaRepository<Boat, Long> {}
Then the http response:
{
"_embedded":{
"boats":[
{
"id":1,
"name":"Boat 1",
"description":"A brief description of the boat 1",
"type":{
"id":1,
"name":"Motorboats"
},
"_links":{
//...
}
},
// ...
]
}
}