试水mongodb er

1)data ready

var a = {"name":"zhekou","CharDate":"2015-12-01","Detail":
[{"DetailID":1,"Abstract":"1a","LenderAmt":20,"DebtAmt":0,"BaseAmt":20},
{"DetailID":2,"Abstract":"2a","LenderAmt":3,"DebtAmt":0,"BaseAmt":3},
{"DetailID":3,"Abstract":"3a","LenderAmt":4,"DebtAmt":0,"BaseAmt":4}]
}

db.Voucher.insert(a);

var a = {"name":"zhekou","CharDate":"2015-12-01","Detail":
[{"DetailID":4,"Abstract":"1a","LenderAmt":56,"DebtAmt":0,"BaseAmt":56},
{"DetailID":5,"Abstract":"2a","LenderAmt":34,"DebtAmt":0,"BaseAmt":34},
{"DetailID":6,"Abstract":"3a","LenderAmt":87,"DebtAmt":0,"BaseAmt":87}]
}
db.Voucher.insert(a); 

2)function

db.Voucher.aggregate(
{$unwind:"$Detail"},
{$match:{"Detail.Abstract":/a/}},
{$project:{ _id:0, amount: "$Detail.BaseAmt",Abstract:"$Detail.Abstract"}},
{$group:{_id:"$Abstract",total:{$sum:"$amount"}}}
)

2_1)

$match:过滤后再分组，Detail.Abstract，虽然用了unwind打开，但是还是要用Detail.前缀引用

$project:重命名

$:引用

$group:分组，_id:分组by**,$sum:相加

3)result

/* 0 */
{
"result" : [
{
"_id" : "3a",
"total" : 91
},
{
"_id" : "2a",
"total" : 37
},
{
"_id" : "1a",
"total" : 76
}
],
"ok" : 1
}

试水mongodb er

原文：http://www.cnblogs.com/Ellfelo/p/aggregate_unwind.html