如何在 Firebase 中创建排行榜？

Question

There is a point system in my application. I want to create an ordered list of points in a part. It will be in order from highest score to lowest score. In the code I wrote, this system does not work correctly. not ranked from highest to lowest score. Newly rated users appear at the top. How can I fix this problem? I want it sorted from highest score to lowest score.

Scoreboard class:

DatabaseReference UsersRef, RatingsRef;
int currentpage = 1 ;
static final int total_ITEMS = 10 ;
RecyclerView scorrecy ;

UsersRef = FirebaseDatabase.getInstance().getReference().child("Users");
RatingsRef = FirebaseDatabase.getInstance().getReference().child("Ratings");
RatingsRef.keepSynced(false);

getScor();

  public void getScor(){

        FirebaseRecyclerOptions<ScorModel> options =
                new FirebaseRecyclerOptions.Builder<ScorModel>()
                        .setQuery(RatingsRef.orderByChild("puan").limitToLast(currentpage * total_ITEMS),ScorModel.class)
                        .build();

        FirebaseRecyclerAdapter<ScorModel,ScorViewHolder> adapter
                =new FirebaseRecyclerAdapter<ScorModel, ScorViewHolder>(options)
        {

            @Override
            protected void onBindViewHolder(@NonNull final ScorBoard.ScorViewHolder holder, int position, @NonNull ScorModel model) {
                final String visit_user_id = getRef(position).getKey();  

                UsersRef.child(visit_user_id).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                            if (dataSnapshot.hasChild("isim")){
                                final String myUsername = dataSnapshot.child("isim").getValue().toString();
                                holder.userName.setText(myUsername);
                            }

                    }

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

                    }
                });
                RatingsRef.child(visit_user_id).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        if (dataSnapshot.hasChild("puan")){
                            final String myPoint = dataSnapshot.child("puan").getValue().toString();
                            holder.userPoint.setText(myPoint+" "+"Puan");
                        }else  {
                            holder.userPoint.setText("0 Puan");
                        }

                    }

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

                    }
                });

            }

            @NonNull
            @Override
            public ScorBoard.ScorViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
                View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.scorboard_model_layout,viewGroup,false);
                ScorBoard.ScorViewHolder viewHolder = new ScorBoard.ScorViewHolder(view);
                return  viewHolder;
            }
        };

        adapter.startListening();
        scorrecy.setAdapter(adapter);

    }

    public static class ScorViewHolder extends RecyclerView.ViewHolder{
        TextView  userName , userPoint;
        View mView;

        public ScorViewHolder(@NonNull View itemView) {
            super(itemView);
            mView= itemView;

            userName =itemView.findViewById(R.id.rank_username);
            userPoint =itemView.findViewById(R.id.point);
        }
    }

ScorModel;

  public String scor, username , currentUserID ;

    public ScorModel(){

    }

    public ScorModel(String scor,String username , String currentUserID) {
        this.scor= scor;
        this.username = username;
        this.currentUserID = currentUserID;

    }

  public String getScor() {
        return scor;
    }

    public void setScor(String scor) {
        this.scor = scor;
    }


    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

Myy DB Ratings;

enter image description here

Update:

RatingsRef = FirebaseDatabase.getInstance().getReference().child("Ratings");
      
 RatingsRef.child(currentUserID).child("Ratings").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                double sum =  0.0;

                try {
                    for (DataSnapshot ds: dataSnapshot.getChildren()) {
                        Map<String,Object> map = (Map<String, Object>) ds.getValue();
                        Object rating =  map.get("rating");
                        Double pvalue = Double.parseDouble(String.valueOf(rating));
                        sum += pvalue;



                        Map userpoint = new HashMap();
                        userpoint .put("puan", String.valueOf(sum));

                        RatingsRef.child(currentUserID).updateChildren(userpoint );


                    }
                }catch (Exception e){

                }


            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
                throw databaseError.toException(); // don't ignore errors
            }
        });

Answer 1

You cannot get the desired results, because your puan field holds a value of type string and not a number. One thing to remember is that when you order strings the results are ordered lexicographically . For example, 10 is placed before 2. See an example below:

1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2, 20, 21, 3

So the best option that you have is to change the type of the field to be number and not string.