Question

基本上我想根据月份对民意调查进行分组。

我的模特：

push()

示例数据：

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);

但是当我尝试使用类似于https://stackoverflow.com/a/38596913/5871771

的猫鼬创建群组时

我收到[ { "_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" } ] } ] } ]错误

我还尝试使用以下代码进行基本分组

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

但我得到同样的错误

Answer 1

长时间搜索后找到解决方案：

必须首先$unwind数组，以便mongodb可以访问数组对象

以下代码工作正常

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：

MongoError：在嵌套文档中对记录进行分组时，无法将BSON类型丢失转换为Date

1 个答案: