如何获得猫鼬分组数据的总和

Question

I have a collection includes log data.

[
   {
      "logType":1,
      "created_at": 2015-12-15 07:38:54.766Z
   },
   ..
   .. 
   ..,
   {
      "logType":2,
      "created_at": 2015-13-15 07:38:54.766Z
   }
]

I want group by created_at field and get group element counts.

My goal is show infographic which includes total logs count by weekly.

Answer 1

You can group by week using $week and $year :

db.logs.aggregate([
    {
      $group:{
         _id: {
           year: { $year:"$created_at" },
           week: { $week:"$created_at" }
         },
         count: { $sum:1 }
      }
    }
])