MongoError：在对嵌套文档中的记录进行分组时，无法从缺少的 BSON 类型转换为日期

Posted 2023-03-11

【中文标题】MongoError：在对嵌套文档中的记录进行分组时，无法从缺少的 BSON 类型转换为日期

【英文标题】：MongoError: can't convert from BSON type missing to Date while Grouping records in nested documents

【发布时间】：2017-10-24 16:10:10

【问题描述】：

基本上我想按月份对投票进行分组。

我的模特：

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var voteSchema = new Schema(
    ip: String,
    votedOn:  type: Date, default: Date.now 
);

var choiceSchema = new Schema(
    text: String,
    votes: [voteSchema]
);

var PollSchema = new Schema(
    question:  type: String, required: true ,
    choices: [choiceSchema]
);

module.exports = mongoose.model('Polls', PollSchema);

样本数据：

[
    
        "_id": "5914056440bfac03711966ad",
        "choices": [
            
                "text": "c3",
                "_id": "5914056440bfac03711966af",
                "votes": [
                    
                        "ip": "::1",
                        "_id": "5914058040bfac03711966b4",
                        "votedOn": "2017-05-11T06:32:32.685Z"
                    
                ]
            ,
            
                "text": "c1",
                "_id": "5914056440bfac03711966ae",
                "votes": [
                    
                        "ip": "::1",
                        "_id": "587dec8eaccc4b036a193a8f",
                        "votedOn": "2017-01-17T10:06:06.012Z"
                    
                ]
            
        ]
    ,
    
        "_id": "5914057540bfac03711966b0",
        "choices": [
            
                "text": "b3",
                "_id": "5914057540bfac03711966b3",
                "votes": [
                    
                        "ip": "::1",
                        "_id": "591d6b8caccc4b036a193a8e",
                        "votedOn": "2017-05-18T09:38:20.363Z"
                    
                ]
            ,
            
                "text": "b2",
                "_id": "5914057540bfac03711966b2",
                "votes": [
                    
                        "ip": "::1",
                        "_id": "591d69b7accc4b036a193a8d",
                        "votedOn": "2017-05-18T09:30:31.708Z"
                    ,
                    
                        "ip": "::1",
                        "_id": "587dec9aaccc4b036a193a90",
                        "votedOn": "2017-01-17T10:06:18.137Z"
                    
                ]
            ,
            
                "text": "b1",
                "_id": "5914057540bfac03711966b1",
                "votes": [
                    
                        "ip": "::1",
                        "_id": "587decafaccc4b036a193a91",
                        "votedOn": "2017-01-17T10:06:39.809Z"
                    
                ]
            
        ]
    
]

但是当我尝试使用类似于https://***.com/a/38596913/5871771 的猫鼬创建组时

我收到MongoError: can't convert from BSON type missing to Date 错误

我也尝试使用以下代码进行基本分组

Poll.aggregate( 
            $group : 
                _id :  month:  $month: "$votes.votedOn" , day:  $dayOfMonth: "$votes.votedOn" , year:  $year: "$votes.votedOn"  
             
        , function(err, d) 
            if (err) 
                throw err;
            
            console.log(JSON.stringify(d, null, 4));
        
    );

但是我遇到了同样的错误

【参考方案1】：

经过长时间的搜索找到了解决方案：

必须首先$unwind 数组，以便mongodb 可以访问 数组对象

以下代码运行良好

Poll.aggregate(

     // Un-wind the array's to access filtering 
      $unwind: "$choices" ,
      $unwind: "$choices.votes" ,
      $unwind: "$choices.votes.votedOn" ,

     // Group results to obtain the matched count per key
      $group: 
         _id :  month:  $month: "$choices.votes.votedOn" , year:  $year: "$choices.votes.votedOn"  ,
         count:  "$sum": 1 
     , function(er, d) 
        console.log(d)
     
 )

这将导致我需要的东西

[ 
     _id:  month: 1, year: 2017 , count: 3 ,
     _id:  month: 5, year: 2017 , count: 3  
]

请参阅$unwind 的文档：