Java 如何从Firestore获取DocumentReference字段？

我正在尝试从google Firestore检索对象，这是对象：

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

由于我添加了atribute soat im getting Errors im，因此我使用该类来反序列化对象：

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

这段代码用于从Firestore检索所有汽车对象

     @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;
    }

编辑：刚刚尝试了这个方法，仍然得到相同的错误

    @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;
    }

现在我从Firestore电话里得到了这个

[{"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":

---

基本上，您必须创建一个类来反序列化数据库引用，在这种情况下，类名将是

SOAT

，并使用它来取消对数据库的引用

@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;
}

然后，当从FireBase检索信息时，您必须发出以下请求，以指定要映射的对象的类型

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;
    }

---

您可能想尝试单独从快照中取出每个字段，而不是使用toObjut.To尝试，仍然得到相同的错误，感谢您的帮助，不管怎样，扫描显示代码，在那里你得到个人<代码> SOAT字段和在这种情况下得到的错误。我不确定这将如何抛出一个

stackoverflowerrror

caremp=doc.toObject（Car.class）当我使用这部分代码时，它从第一张图像中显示的Firebase对象检索整个信息，并使用
Car
类对其进行映射，因此我永远不会单独获得
soat
。
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;
    }

{
    "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"
    }
  }