字段"$ name"位于必须是一个累加器对象 [英] The field "$name" must be an accumulator object

问题描述

我有一个查询，当我使用 $ group 错误显示字段"$ name必须是累加器对象""，如果删除归档的"$ name"，则一切正常，并且我尝试仅使用"name"而不是"$ name"，并且错误继续.

I have a query and when I use a $group a error shows "the field "$name must be an accumulator object", if if remove the filed "$name" all works well and i have tried to use only "name" instead of "$name" and the error continues.

   User.aggregate([
    {
      $match: {
        "storeKey": req.body.store        
      }
  },
  {
      $group: {
          "_id": "$_id",          
          "name": "$name",              
          "count": {
              "$sum": 1
          },
          "totalValue": {
              "$sum": "$value"
          }      
      }
  },
  {
    $sort: sort
  },
  {
     $skip: req.body.limit * req.body.page
  },
  {
     $limit: req.body.limit
  }
])...

推荐答案

有些聚合运算符只能在

There are some aggregation operators that can only be used in $group aggregation and named as $group accumulators

就像您使用> $sum 在这里，您还必须使用name键

Just as you used $sum here you have to use for the name key as well

{ "$group": {
  "_id": "$_id",
  "name": { "$first": "$name" },  //$first accumulator
  "count": { "$sum": 1 },  //$sum accumulator
  "totalValue": { "$sum": "$value" }  //$sum accumulator
}}

累加器就像元素数组一样，其累加为数组. $ first->给出名称组中第一个名称

Accumulator is like array of Elements its Accumulates as Array. $first -> gives 1st name that goes in the group of names

示例: 因此，如果您具有$_id相同但不同的名称["Darik","John"] 指定$first将为Darik&类似地，$last将给约翰

Example: so if you have $_id same but different name ["Darik","John"] specifying $first will give Darik & similarly $last will give John

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