数组中对象的MongoDB聚合总和 [英] MongoDB Aggregation Sum on Objects in Array

问题描述

我已经看到了很多关于如何求和数组中数组对象的属性的答案，但是我试图跨文档对一个数组中对象的单个属性求和.例如，给定此文档结构:

I've seen a lot of answers on how to sum properties of objects in arrays within the array, but I'm trying to sum individual properties on an object in an array across documents. For example, given this document structure:

{
   "id": 1,
   "stats": [
     {
       "number": 100,
       "year": 2014
     },
     {
       "number": 200,
       "year": 2015
     }
]
},


{
   "id": 2,
   "stats": [
     {
       "number": 50,
       "year": 2014
     },
     {
       "number": 75,
       "year": 2015
     }
]
}

所需的输出将是:

{
   "stats": [
     {
       "number": 150,
       "year": 2014
     },
     {
       "number": 275,
       "year": 2015
     }
}

我不想对2014和2015的number属性求和，我想对两个文档在2014年进行求和.

I don't want to sum the number property of 2014 and 2015, I want to sum it across 2014 for both documents.

推荐答案

db.test.aggregate([
   {  $unwind: "$stats" },
   {
        $group: {
            _id:"$stats.year",
            number:{$sum:"$stats.number"}
        }
    },
    { 
        $group: {
          _id: 0,  
          stats:{ $push:  {year:"$_id",number:"$number"}}
        }
    },
    {  
        $project:{stats:1,_id:0}
    } ])

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