FireBase的orderBychild（）.Equals未获取任何数据

Question

mDatabase = FirebaseDatabase.getInstance().getReference("archive");
mDatabase.orderByChild("_age").equalTo("20").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        value = dataSnapshot.getValue(String.class);
        tSResult.setText(value);
    }

    @Override
    public void onCancelled(DatabaseError error) {

        Log.w(TAG, "Failed to read value.", error.toException());
    }
});

Firebase数据库。

Answer 1

Query  query = mDatabase.orderByChild("_age").equalTo("20");
            query .addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if(dataSnapshot.getChildrenCount() > 0){
                        System.out.println("count : "+ dataSnapshot.getChildrenCount());
                        for(DataSnapshot child : dataSnapshot.getChildren()){
                           value = child.getValue(String.class);
                            tSResult.setText(value);
                        }
                    }

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });