从 Firebase Firestore 获取文档的一部分到对象中

Question

I'm creating one document with this data:

{
   "fields":{
      "meta":{
         "mapValue":{
            "fields":{
               "semana":{
                  "stringValue":"Semana XX"
               },
               "fecha":{
                  "stringValue":"20191209"
               },
               "titulo":{
                  "stringValue":"Lunes II de Adviento"
               },
               "mensaje":{
                  "stringValue":""
               },
               "tiempo":{
                  "integerValue":1
               }
            }
         }
      },
      "lh":{
         "mapValue":{
            "fields":{
               "0":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/0/0108022"
               },"1":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/1/0108022"
               },"2":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/2/0100022"
               },"3":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/3/0100022"
               },"4":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/4/0100022"
               },"5":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/5/0100022"
               },"6":{
                  "referenceValue":"projects/miproject/databases/(default)/documents/es/v1/liturgia/lh/6/0100022"
               }
            }
         }
      }
   }
}

The document is created without a problem.

Now, in Android, I need to fill two types of objects:

a. With the key meta I need to populate one object of type MetaLiturgia , and

b.I take one of the references to populate another object.

My problem is in a , I can't populate the MetaLiturgia object.

Code

    DocumentReference calRef = db.collection(CALENDAR_PATH).document(fechaYY).collection(fechaMM).document(fechaDD);
    calRef.addSnapshotListener(new EventListener<DocumentSnapshot>() {
        @Override
        public void onEvent(@Nullable DocumentSnapshot calSnapshot,
                            @Nullable FirebaseFirestoreException e) {
            if (calSnapshot != null && calSnapshot.exists()) {
                Log.d(TAG,calSnapshot.toString());
                Log.d("meta",calSnapshot.get("meta").toString());
                /* (a) Error here, line 120 is below line*/
                mMeta = (MetaLiturgia) calSnapshot.getData();
                DocumentReference dataRef=calSnapshot.getDocumentReference("lh.1");
                if (e != null || dataRef==null) {
                    launchVolley();
                    return;
                }
                dataRef.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
                    @Override
                    public void onSuccess(DocumentSnapshot dataSnapshot) {
                        /*(b) No problem here*/
                        mBreviario = dataSnapshot.toObject(Breviario.class);
                        showData();
                    }
                });
            } else {
                launchVolley();
            }
        }
    });

I can see the data in the Log:

D/meta: {fecha=20191209, tiempo=1, semana=Semana XX, titulo=Lunes II de Adviento, mensaje=}

But I'm having this error:

2019-12-09 10:44:52.233 25121-25121/org.my.app E/AndroidRuntime: FATAL EXCEPTION: main Process: org.my.app, PID: 25121 java.lang.ClassCastException: java.util.HashMap cannot be cast to org.my.app.model.MetaLiturgia at org.my.app.activities.OficioActivity$1.onEvent(OficioActivity.java:120)

How I can do this?

Answer 1

You are getting the following exception:

E/AndroidRuntime: FATAL EXCEPTION: main Process: org.my.app, PID: 25121 java.lang.ClassCastException: java.util.HashMap cannot be cast to org.my.app.model.MetaLiturgia

When using the following line of code:

mMeta = (MetaLiturgia) calSnapshot.getData();

Because when you are calling calSnapshot.getData() the type of object that is returned is a HashMap and not a MetaLiturgia and there is no way in Java you can cast an object of type HashMap to MetaLiturgia . Since that object is a HashMap , you should get it accordingly. But please also note that your fields property is a HashMap of HashMaps . So you should iterate twice in order to get the desired data.