java - 是否有任何查询可以查找 Firebase 数据库(Android Studio)中同名子项的数量总和？

Question

查询同名商品的数量总和... enter image description here

final Query query2 = billdata.orderByChild ( "name" );
        query2.addListenerForSingleValueEvent ( new ValueEventListener ()
        {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot)
            {
                for ( DataSnapshot dataSnapshot1 : dataSnapshot.getChildren())
                {
                    int total1 = Integer.parseInt ( String.valueOf ( dataSnapshot1.child ( "qty" ).getValue () ) );
                    int sum=0;
                    sum=sum+total1;
                    Toast.makeText (this,"Whole Total"+sum,Toast.LENGTH_LONG ).show ();

Answer 1

没有特定的查询来计算子项的总和，你想这样做

// declare an int variable in global like this  
             int globalsum=0;

    final Query query2 = billdata.orderByChild ( "name" );
            query2.addListenerForSingleValueEvent ( new ValueEventListener ()
            {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot)
                {
                    int sum=0;
                    for ( DataSnapshot dataSnapshot1 : dataSnapshot.getChildren())
                    {
                        int total1 = Integer.parseInt ( String.valueOf ( dataSnapshot1.child ( "qty" ).getValue () ) );

                        sum=sum+total1;
                        globalsum=sum;
                        Toast.makeText (this,"Whole Total"+sum,Toast.LENGTH_LONG ).show ();