Mangoos平均评级返回null，如何在mongoDB中使用Aggregator函数

问题描述

我在MongoDB中收集了以下文档，我试图获取评分和计数的平均值，但始终获取Null作为平均值。请帮忙，我还检查了评级字段类型是否为数字，该数字应返回5作为平均值

[
    {
        "create_date": "2020-08-10T16:40:55.838Z","_id": "5f31789c41b89e1b1c47bf4e","first_name": "dd","last_name": "sds","email": "[e-mail]","phone": "23123212","services": [
            {
                "_id": "5f3181399c22ce892c29e916","amount": 10,"service": "5f2fc9fc54ed4528c899ca13"
            }
        ],"address": [
            {
                "_id": "5f341872ef6a6a44f0a307f5","street": "[e-mail]","city": "asdfgh","state": "czxczx","postal": "324324"
            },{
                "_id": "5f341877ef6a6a44f0a307f6","postal": "324324"
            }
        ],"ratings": [
            {
                "_id": "5f356ee07f72d453d04e7bdf","rating": 5,"jobId": "5f34233efe7fca44447a8454","ratingBy": "5f3172905a9f542cccf8205f"
            },{
                "_id": "5f356f44bb933d0c38999ac5","ratingBy": "5f3172905a9f542cccf8205f"
            }
        ]
    }
]

并尝试从评分中获取计数和平均值，但是它始终返回NULL，我只需要评分数和平均值即可。

我尝试使用下面的代码来获得相同的结果，但未按预期工作，我查看了所有要求相同的帖子数，但仍然没有得到我的结果，不知道我在哪里弄错了。

let docs = await Provider.aggregate([
  { $match: { _id: ObjectId("5f31789c41b89e1b1c47bf4e") } },{
    $group: {
      _id: "$ratings._id",average: { $avg: "$ratings.rating" },},]);

预先感谢您的帮助。

解决方法

我发现下面的代码对我来说很有效

  let userInfo = await Provider.aggregate([
      { $match: { _id: ObjectId(req.params.userid) } },{
        $addFields: {
          averageRating: {
            $avg: "$ratings.rating",},]);