Get data from firebase realtime between table to recycler view

问题

I am having problem reading data from Firebase. But, I just can get single data but, I need to get list of that data. Since it is my first work using Firebase. I have only used SQL in the past.

Here is My Firebase Structure.

"UserEO" : {
    "RZ5piQEWcoSonDYPu3NSKBrXTbW2" : {
      "-LdK1ZgjaKvXFjUeq-Yj" : {
        "keyUID" : "RZ5piQEWcoSonDYPu3NSKBrXTbW2"
      },
      "-LdK264lPX9eBBzYe0m4" : {
        "keyUID" : "RZ5piQEWcoSonDYPu3NSKBrXTbW2"
      }
    }   
},

"eventOrganizer" : {
    "-LdK1ZgjaKvXFjUeq-Yj" : {
      "deskripsi" : "USMA is .. ",
      "namaGrup" : "UKM USMA",
      "website" : "ukm.usma.blogspot.com"
    },
    "-LdK264lPX9eBBzYe0m4" : {
      "deskripsi" : "LPM KOMPEN is ..",
      "namaGrup" : "UKM LPM KOMPEN",
      "website" : ""
    }   },   

"users" : {
    "RZ5piQEWcoSonDYPu3NSKBrXTbW2" : {
      "email" : "kiranana@gmail.com",
      "nama" : "kirana"
    }   
}

Here is my code, I want to select group eventOrganizer that user joining.

    userId=auth.getCurrentUser().getUid();

    recyclerView = (RecyclerView) findViewById(R.id.rv_grupeo);
    layoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
    recyclerView.setLayoutManager(layoutManager);
    grupEOModelList = new ArrayList<>();
    adapter = new GrupEOAdapter(grupEOModelList,GrupEO.this);
    recyclerView.setAdapter(adapter);

    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("UserEO").child(userId);
    databaseReference.addValueEventListener(valueEventListenerAdmin);
}

ValueEventListener valueEventListenerAdmin = new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        String getKey = null;
        if (dataSnapshot.exists()){
            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                getKey = snapshot.getKey();
            }
            final DatabaseReference databaseReferenceEO = FirebaseDatabase.getInstance().getReference("eventOrganizer");
            databaseReferenceEO.orderByKey().equalTo(getKey).addValueEventListener(valueEventListener);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

    }
};
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        grupEOModelList.clear();
        if (dataSnapshot.exists()){
            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                GrupEOModel grupEOModel = snapshot.getValue(GrupEOModel.class);
                grupEOModelList.add(grupEOModel);
            }
            adapter.notifyDataSetChanged();
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

    }
};}

Thanks in advance.

回答1:

I guess the problem is here:

final DatabaseReference databaseReferenceEO = FirebaseDatabase.getInstance().getReference("eventOrganizer");
        databaseReferenceEO.orderByKey().equalTo(getKey).addValueEventListener(valueEventListener);

I don't know it it's a good ideia to embedd a valueListener inside OnDataChange, I would suggest you remove this and work with callbacks. Just convert UserEO in a list using this:

ArrayList<UserEO> td = (ArrayList<UserEO>) dataSnapshot.getValue();

return it in a callback, then you can call for each key an method with your valueEventListener.

I also would like to suggest you a simplification. You can add another child inside users like, events: {"LdK1ZgjaKvXFjUeq", "-LdK264lPX9eBBzYe0m4"}, so each user will have a list of events key, pretty straightfoward.
The key of a good use of NoSQL is to design well your data, optimizing it for queries, I can see you're still thinking like SQL tables, but it's ok since you're still learning.

回答2:

you can get list of data like this :-

ArrayList<Chat> mChat = new ArrayList<>();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference(chatTableName);
reference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    mChat.clear();
                    Chat chat = null;
                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        chat = snapshot.getValue(Chat.class);
                        mChat.add(chat);
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });

来源：https://stackoverflow.com/questions/55872600/get-data-from-firebase-realtime-between-table-to-recycler-view