android - 在 Android 上过滤 Firebase 数据库 DataSnapshot 子级

Question

我想在 Android 上查询来自 Firebase 的数据。这是我的数据

这是我的 Android Studio 代码:

Firebase myFirebaseRef = new Firebase("https://....../myCoffee/"+phone+"");
            myFirebaseRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot snapshot) {
                    int size= (int) snapshot.getChildrenCount();
                    txtMyCoffee.setText(""+size);
                          }
                @Override
                public void onCancelled(FirebaseError firebaseError) {
                }
            });

问题: child 的总数是 4。我如何过滤 child 以只计算“coffeeNo”为“Acoffee”的 child ？

Answer 1

Just improve your query to get only the result your are looking for:

DatabaseReference databaseRef = FirebaseDatabase.getInstance().getReferenceFromUrl("https://....../myCoffee/"+phone+"");
Query acoffeeQuery = databaseRef.orderByChild("coffeeNo").equalTo("Acoffee");
acoffeeQuery.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        final int size = (int) snapshot.getChildrenCount();
        //size is equal to 2
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {}
});

This way, you do not have to loop over all results and you do not haveto implement a counter manually.