在Firebase数据库(安卓工作室)中有没有查询同名孩子的数量总和

Question

查询以查找具有相同名称的项目数量的总和。。。在此处输入图像描述

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 ();