Mongoose 兩個表關聯查詢aggregate 以及 Mongoose中獲取ObjectId

Mongoose 兩個表關聯查詢aggregate

通常兩個表關聯查詢的時候，是一種一對多的關系，比如訂單與訂單詳情就是一對多的關系，一個訂單下面有多個商品

數據模擬

首先我們先將數據模擬出來，先選擇數據庫

use eggcms

db.order.insert({"order_id":"1","uid":10,"trade_no":"111","all_price":100,"all_num":2})
db.order.insert({"order_id":"2","uid":7,"trade_no":"222","all_price":90,"all_num":2})
db.order.insert({"order_id":"3","uid":9,"trade_no":"333","all_price":20,"all_num":6})

db.order_item.insert({"order_id":"1","title":"商品鼠標 1","price":50,num:1})
db.order_item.insert({"order_id":"1","title":"商品鍵盤 2","price":50,num:1})
db.order_item.insert({"order_id":"1","title":"商品鍵盤 3","price":0,num:1})
db.order_item.insert({"order_id":"2","title":"牛奶","price":50,num:1})
db.order_item.insert({"order_id":"2","title":"酸奶","price":40,num:1})
db.order_item.insert({"order_id":"3","title":"礦泉水","price":2,num:5})
db.order_item.insert({"order_id":"3","title":"毛巾","price":10,num:1})

代碼演示：使用Mongoose來實現order集合和order_item集合的關聯查詢

Mongoose中aggregate管道的語法跟原生MongoDB的語法是一樣的

db.order.aggregate([
  {
    $lookup:
      {
        from: "order_item",
        localField: "order_id",
        foreignField: "order_id",
        as: "items"
      }
  }
])

第一步：創建model文件夾並且創建db.js（連接數據庫）

const mongoose = require('mongoose');

mongoose.connect('mongodb://127.0.0.1:27017/eggcms', { useNewUrlParser: true }, (err) => {
  if(err){
    return console.log(err);
  }
  console.log('數據庫連接成功')
});

module.exports = mongoose

第二步：分別創建order.js和order_item.js這兩個model模塊

var mongoose = require('./db.js');

var OrderSchema=mongoose.Schema({
  order_id: String,
  uid: Number,
  trade_no: String,
  all_price: Number,
  all_num: Number
})

module.exports = mongoose.model('Order',OrderSchema,'order');

var mongoose = require('./db.js');


var OrderItemSchema = mongoose.Schema({
  order_id: String,
  title: String,
  price: Number,
  num: Number
})

module.exports = mongoose.model('OrderItem',OrderItemSchema,'order_item');

第三步：在app.js中進行兩個集合的關聯查詢

let OrderModel = require('./model/order.js');

// order表關聯order_item
OrderModel.aggregate([
  {
    $lookup:
      {
        from: "order_item",
        localField: "order_id",
        foreignField: "order_id",
        as: "items"
      }
  }
], (err, docs) => {
  if(err){
    return console.log(err)
  }

  console.log(JSON.stringify(docs))
})

將查詢出來的數據復制出來解析成JSON格式會更清晰，找一個在線格式化的網址即可，實際項目中不需要

 

 

 

Mongoose 兩個表關聯查詢aggregate練習

需求：查詢order_item，找出商品名稱是酸奶的商品，酸奶這個商品對應的訂單的訂單號以及訂單的總價格

第一種實現方式

思路：首先通過酸奶這個商品的_id查詢order_item集合，找到這個商品，並且獲取商品中的order_id，然后再通過order_id去查詢order集合

let OrderItemModel = require('./model/order_item.js');

let OrderModel = require('./model/order.js');

OrderItemModel.find({"_id":"5cde69c24a988180bdf060b0"}, (err,docs) => {

  // console.log(docs);

  let order_item = JSON.parse(JSON.stringify(docs));

  let order_id = order_item[0].order_id;


  OrderModel.find({"order_id":order_id}, (err,order) => {
    order_item[0].order_info = order[0];
    console.log(order_item)
  })
})

第二種實現方式 

思路：直接使用$match：條件匹配，然后進行兩個表關聯查詢

mongoose中獲取ObjectId （mongoose.Types.ObjectId）

let OrderItemModel = require('./model/order_item.js');
let mongoose = require('mongoose');

OrderItemModel.aggregate([
  {
    $lookup:
      {
        from: "order",
        localField: "order_id",
        foreignField: "order_id",
        as: "order_info"
      }
  },{
    $match:{_id: mongoose.Types.ObjectId('5cde69c24a988180bdf060b0')}
  }

], (err,docs) => {
  if(err){
    console.log(err)
    return;
  }
  console.log(JSON.stringify(docs))
})