猫鼬聚合中未显示字段 [英] Field not showing in Mongoose aggregation

问题描述

我正在尝试统计所有不同的部门.我希望结果包含deptType，deptName和计数.分组有效，结果显示deptType和dCount，但不显示deptName.知道为什么吗?

I'm trying to get a count of all distinct departments. I'd like the results to contain the deptType, deptName and the count. The grouping works, and results show deptType and dCount, but not deptName. Any idea why?

我的数据如下:

{
  "_id": "10280",
  "city": "NEW YORK",
  "state": "NY",
  "departments": [
         {"departmentType":"01",
          "departmentHead":"Peter"},
         {"departmentType":"02",
          "departmentHead":"John"}
  ]
},
{
  "_id": "10281",
  "city": "LOS ANGELES",
  "state": "CA",
  "departments": [
         {"departmentType":"02",
          "departmentHead":"Joan"},
         {"departmentType":"03",
          "departmentHead":"Mary"}
]
}

和我的Mongoose聚合命令如下:

and my Mongoose aggregate command like this:

Departments.aggregate(
{  
$project : {"departments.deptType" : 1,
        "departments.deptName" : 1,
        "dCount" : 1  } 
},
{ 
    $match: {"departments.deptType": {$exists: true}} 
},
{  
    $unwind: "$departments" 
},
{ 
    $group: {
        _id: "$departments.deptType",
         dCount: { $sum: 1 },
    }
},
{
$match: { dCount: { $gt: 5 }   }
},
{ $sort: { dCount: -1 } },
{ $limit : 50 },  

function(err, dbres) {}
);

谢谢大家.

推荐答案

对不起，很傻:

(...)
$group: {
    _id : { dType : "$departments.deptType", 
            dName : "$departments.deptName" 
          },
   dCount: { $sum: 1 },
}
(...)

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