Mongodb-mongoose collections undefined - node.js

Question

I am new and practicing Mongoose and Mongodb connection. I successfully connect my database to my local machine and get log confirmations. I am trying get my collection without passing mongoose Schema but I am getting error: TypeError: Cannot read property 'collection' of undefined. I don't know what I am doing wrong.
Here is code:
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

You're trying to access the DB before the connection is established to MongoDB. ( Connecting to DB is asynchronous code )
Also, Read - 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);
});
Or
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
})
});
});