Mongodb聚合框架和时间戳

问题描述

我有一个收藏集

{ "_id" : 1325376000, "value" : 13393}
{ "_id" : 1325462400, "value" : 13393}

ObjectIds是Unix Timestamp，并手动存储为Number （插入时）。

ObjectIds are Unix Timestamp and are storing as Number manually.(at insert time).

现在我正在寻找一种可以使用Aggregation Framework计算每个月的值总和的解决方案。

now I'm searching for a solution that i could calculate sum of values for each month with Aggregation Framework.

推荐答案

以下是通过编程方式生成聚合管道的一种方法：

Here is a way you can do it by generating the aggregation pipeline programmatically:

numberOfMonths=24;   /* number of months you want to go back from today's */
now=new Date();
year=now.getFullYear();
mo=now.getMonth();
months=[];
for (i=0;i<numberOfMonths;i++) {
      m1=mo-i+1; m2=m1-1;
      d = new Date(year,m1,1);
      d2=new Date(year,m2,1);
      from= d2.getTime()/1000;
      to= d.getTime()/1000;
      dt={from:from, to:to, month:d2};  months.push(dt);
}
prev="$nothing";
cond={};
months.forEach(function(m) {
      cond={$cond: [{$and :[ {$gte:["$_id",m.from]}, {$lt:["$_id",m.to]}  ]}, m.month, prev]};
      prev=cond;
} );

/* now you can use "cond" variable in your pipeline to generate month */
db.collection.aggregate( { $project: { month: cond , value:1 } },
                         { $group: {_id:"$month", sum:{$sum:"$value"} } }
)

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