从 mongoDB 获取计数

Question

我正在使用芒果创建问答网站，express.So有两种问答模式。

我的问答模式是这样的，

const questionSchema = mongoose.Schema({
_id : mongoose.Schema.Types.ObjectId,
user: { type:mongoose.Schema.Types.ObjectId, ref: 'User', required: true},
title: {type: String , required:true},
question: {type: String , required:true},
tags: {type: Array , required: true},
time : { type : Date, default: Date.now },
vote: {type: Number, default: 0},
views: {type: Number, default: 0}     });


const answerSchema = mongoose.Schema({
_id : mongoose.Schema.Types.ObjectId,
user: { type:mongoose.Schema.Types.ObjectId, ref: 'User', required: true},
question:{ type:mongoose.Schema.Types.ObjectId, ref: 'Question', required: true},
comment: [{type: mongoose.Schema.Types.ObjectId, ref: 'Comment', default: null }],
answer: {type: String, required: true},
vote: {type: Number , default: 0},
time : { type : Date, default: Date.now }   });

这里有很多与 question.My 主页相关的答案获取所有问题 preview.How 以获得与每个问题相关的答案的计数？

Answer 1

因为你的 questionSchema 与 Answers collection 没有任何直接关系（比如不存储 Answers 引用）那么试试这个：

查询:

db.Question.aggregate([
    {
        $lookup:
        {
            from: "Answer",
            localField: "_id",
            foreignField: "question",
            as: "answers"
        }
    }, 
    /** In case if you need all details of question replace 'project' with 'addFields' & remove 'question: 1' */
    { $project: { question: 1, count: { $size: '$answers' } } } 
])

测试：MongoDB-Playground

从 mongoDB 获取计数

Get count number from mongoDB

mongoose

mongodb

express

mongoose-schema