Mongodb-mongoose 集合未定义

Question

我是新手，正在练习 Mongoose 和 Mongodb 连接。我成功地将我的数据库连接到我的本地计算机并获得日志确认。我正在尝试在不通过猫鼬模式的情况下获取我的收藏，但出现错误：TypeError: Cannot read property 'collection' of undefined。我不知道我做错了什么。

代码如下：

require("dotenv").config();
const express = require("express");
const mongoose = require("mongoose");
const { Schema } = mongoose;

const app = express();
mongoose
  .connect(process.env.MONGODB_URI, {
    useUnifiedTopology: true,
    useNewUrlParser: true
  })
  .then(() => console.log("DB Connected!"))
  .catch(err => {
    console.log(err);
  });

var connection = mongoose.connection;

connection.db.collection("bags", function (err, collection) {
  collection.find({}).toArray(function (err, data) {
    console.log(data); // it will print your collection data
  })
});

Answer 1

您正在尝试在与 MongoDB 建立连接之前访问数据库。 （连接DB是异步代码）

另外，请阅读 - https://javascript.info/async-await

---

mongoose
  .connect(process.env.MONGODB_URI, {
    useUnifiedTopology: true,
    useNewUrlParser: true
  })
  .then(() => {
    console.log("DB Connected!");
    var connection = mongoose.connection;
    // run logic once db is connected.
    connection.db.collection("bags", function (err, collection) { 
      collection.find({}).toArray(function (err, data) {
        console.log(data); // it will print your collection data
      })
    });
  })
  .catch(err => {
    console.log(err);
  });

---

或者

mongoose.connection.on('connected', err => { // will trigger connected event when connected to MongoDB
  var connection = mongoose.connection;

  connection.db.collection("bags", function (err, collection) {
    collection.find({}).toArray(function (err, data) {
      console.log(data); // it will print your collection data
    })
  });
});