How do I get a DocumentReference field from Firestore?

Question

Im trying to retrieve an object from a google Firestore, this is the object:

Firestore object

Since i added the atribute soat im getting erros im using this class to deserialize the object:

@Data
public class Car {
    private String plate;
    private String model;
    private long km;
    private boolean available;
    private DocumentReference soat;   
}

And this code to retrieve the all the Car objects from the Firestore

     @Override
    public List<Car> findAll() {
        List<Car> empList = new ArrayList<Car>();
        CollectionReference car = fb.getFirestore().collection("Cars");
        ApiFuture<QuerySnapshot> querySnapshot = car.get();
        try {
            for (DocumentSnapshot doc : querySnapshot.get().getDocuments()) {
                Car emp = doc.toObject(Car.class);
                empList.add(emp);
            }
        } catch (Exception e) {
             e.printStackTrace();
        }
        return empList;
    }

Since i added the property soat im getting this error whe requesting the data

ERROR 7544 --- [nio-8080-exec-7] seErrorMvcAutoConfiguration$StaticView : Cannot render error page for request [request route] and exception [Could not write JSON: Infinite recursion (StackOverflowError); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: com.google.cloud.firestore.FirestoreImpl["options"]->com.google.cloud.firestore.FirestoreOptions["service"]->com.google.cloud.firestore.FirestoreImpl["options"]->com.google.cloud.firestore.FirestoreOptions["service"]->com.google.cloud.firestore.FirestoreImpl["options"]->com.google.cloud.firestore.FirestoreOptions["service"]->com.google.cloud.firestore.FirestoreImpl["options"]... ->com.google.cloud.firestore.FirestoreOptions["credentia ["modulus"])] as the response has already been committed. As a result,

Previously i couldnt make the request properly so i added this to my application.properties

spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false

Edit: just tried this aproach and still getting same error

    @Override
    public List<Car> findAll() {
        List<Car> empList = new ArrayList<Car>();
        CollectionReference car = fb.getFirestore().collection("Cars");
        ApiFuture<QuerySnapshot> querySnapshot = car.get();
        try {
            for (DocumentSnapshot doc : querySnapshot.get().getDocuments()) {
               
                 String plate=doc.getData().get("plate").toString();
                 String model=doc.getData().get("model").toString();
                 long km=Long.parseLong(doc.getData().get("km").toString());
                 boolean available=Boolean.parseBoolean(doc.getData().get("available").toString());
                 DocumentReference soat=(DocumentReference)doc.getData().get("soat");

                Car emp = new Car();
                emp.setAvailable(available);
                emp.setKm(km);
                emp.setModel(model);
                emp.setPlate(plate);
                emp.setSoat(soat);

                empList.add(emp);
            }
        } catch (Exception e) {
             e.printStackTrace();
        }
        return empList;
    }

-------EDIT--------
I have aded this to my application.properties

spring.jackson.serialization.fail-on-self-references=false

And now i get this from the Firestore call

[{"plate":"HEO628","model":"2014","km":75000,"available":true,"soat":{"path":"SOATS/HEO628","parent":{"parent":null,"id":"SOATS","path":"SOATS","firestore":{"firestore":{"firestore":{"firestore":{"firestore":{"firestore":{"firestore":{"firestore":{"firestore":

Answer 1

Basically you have to create a class to deserialice your DatabaseReference, in this case the class name would be SOAT and use it to sotre your reference to the database.

@Data
public class Car {
    private String plate;
    private String model;
    private long km;
    private boolean available;
    private SOAT soat;  
    private Insurance insurance;
    private Techno techno;
}

Then when retrieving the information from FireBase you have to make the following requests in order to specify the kind of object your are going to map.

public List<Car> findAll() {
        List<Car> empList = new ArrayList<Car>();
        CollectionReference car = fb.getFirestore().collection("Cars");
        ApiFuture<QuerySnapshot> querySnapshot = car.get();
        try {
            for (DocumentSnapshot doc : querySnapshot.get().getDocuments()) {

                String plate = doc.getData().get("plate").toString();
                String model = doc.getData().get("model").toString();
                long km = Long.parseLong(doc.getData().get("km").toString());
                boolean available = Boolean.parseBoolean(doc.getData().get("available").toString());
                DocumentSnapshot soatref = fb.getFirestore().collection("SOATS").document(plate).get().get();
                DocumentSnapshot technoref = fb.getFirestore().collection("Technos").document(plate).get().get();
                DocumentSnapshot insuranceref = fb.getFirestore().collection("Insurances").document(plate).get().get();
                SOAT soat = soatref.toObject(SOAT.class);
                Techno techno = technoref.toObject(Techno.class);
                Insurance insurance = insuranceref.toObject(Insurance.class);

                Car emp = new Car();
                emp.setAvailable(available);
                emp.setKm(km);
                emp.setModel(model);
                emp.setPlate(plate);
                emp.setSoat(soat);
                emp.setInsurance(insurance);
                emp.setTechno(techno);

                empList.add(emp);
            }
        } catch (Exception e) {

        }
        return empList;
    }

An then whe calling your API you shold get a proper reference to the Object like this.

{
    "plate": "HEO628",
    "model": "2014",
    "km": 75000,
    "available": true,
    "soat": {
      "expeditionDate": "2020-09-29T06:12:12.000+00:00",
      "carPlate": "HEO628"
    },
    "insurance": {
      "expeditionDate": "2020-10-01T11:12:12.000+00:00",
      "carPlate": "HEO628"
    },
    "techno": {
      "expeditionDate": "2020-09-08T17:00:00.000+00:00",
      "carPlate": "HEO628"
    }
  }