3-10 多表关联查询aggregate

//文章分类
articlecate     
- id
- title
- description
- add_time

article           user
- id                            -id
- cid             -username
- title           -password
- description            -name
- author_id                -age
- author_name            -sex
- content                    -tel
- add_item                -add_time

article的cid和articlecate的id关联
article的author_id和user的id关联

//user.js
const mongoose = require('./db');
const Schema = mongoose.Schema;
const UserSchema =  new Schema({
    username:{type:String,unique:true},
    password:String,
    name:String,
    age:Number,
    sex:String,
    tel:Number,
    status:{
        type:Number,
        status:1
    }
})
module.exports = mongoose.model('User',UserSchema,'user');

//article.js
const mongoose = require('./db');
const Schema = mongoose.Schema;
const ArticleSchema =  new Schema({
    title:{type:String,unique:true},
    cid:{type:Schema.Types.ObjectId},/* 文章分类 */
    author_name:{
        type: String
    },
    author_id:{
        type:Schema.Types.ObjectId /* 用户的id */
    },
    description:String,
    content:String
})
module.exports = mongoose.model('Article',ArticleSchema,'article');

//articlecate.js  文章分类
const mongoose = require('./db');
const Schema = mongoose.Schema;
const ArticlecateSchema =  new Schema({
    title:{type:String,unique:true},
    description:String,
    add_tiem:{
        type:Date
    }
})
module.exports = mongoose.model('Articlecate',ArticlecateSchema,'articlecate');

/* 查询文章的信息 并显示文章的分类  作者的信息 */
var data = ArticleModel.aggregate([
    {$lookup:{
        from:"articlecate",
        localField:'cid',
        foreignField:'_id',
        as:"details"
    }},
    {
        $lookup:{
            from:"user",
            localField:'author_id',
            foreignField:'_id',
            as:'userInfo'
        }
    }
])