来自数组的汇总值

Question

I'm trying to calculate sum of balances divided to currencies. Below example document and my query. Query returns list of currencies with sumBalance equal 0 for all right now. Any advices how to fix it?

{
    _id:5ab94cdb6b106375b6843358   
    credit:
    Array 
0:
    Object
    type:"mastercard" 
    currency:"BRL"
    balance:"4627.56"
1:
    Object
    type:"diners-club-enroute"
    currency:"USD"
    balance:"5222.47"
}

db.mydb.find().forEach( function (x) {
x.credit.balance = parseFloat(x.credit.balance);
db.mydb.save(x);
});
db.mydb.aggregate([
{$unwind: "$credit"},
{$group: {_id: "$credit.currency", sumBalance: {$sum: "$credit.balance"}}}
]).forEach(printjson)

Answer 1

Your problem is that your balance is a String and not a number and $aggregation can't change the data type. I suggest you to update your document to have the balance as Float