MongoDB connection with async/await

connection.js

import { MongoClient } from 'mongodb';
import promisify from 'es6-promisify';

let _connection;

const connect = () => {
  if (!process.env.MONGO_CONNECTION_STRING) {
    throw new Error(`Environment variable MONGO_CONNECTION_STRING must be set to use API.`);
  }

  return promisify(MongoClient.connect)(process.env.MONGO_CONNECTION_STRING);
};

/**
 * Returns a promise of a `db` object. Subsequent calls to this function returns
 * the **same** promise, so it can be called any number of times without setting
 * up a new connection every time.
 */
const connection = () => {
  if (!_connection) {
    _connection = connect();
  }

  return _connection;
};

export default connection;

/**
 * Returns a ready-to-use `collection` object from MongoDB.
 *
 * Usage:
 *
 *   (await getCollection('users')).find().toArray().then( ... )
 */
export async function getCollection(collectionName) {
  const db = await connection();
  return db.collection(collectionName);
}

Why did you not use promisify from the util library of nodejs?

@buoyantair promisify was not available before node 8

This really helped. BTW I had a following error on L38 (getCollection):

TypeError: db.collection is not a function

I used MONGO_CONNECTION_STRING value with database name at the end of URI, but didn't work.

So I edited a little like followings and it worked:

export async function getCollection(collectionName) {
  const db = (await connection()).db(YOUR_DATABASE_NAME);
  return db.collection(collectionName);
}

And no need to make schema because this is why mongo is used for unstructured database storage.

const MongoClient = require('mongodb').MongoClient
require('dotenv').config({ path: `${__dirname}/.env` })


module.exports = async () => {

    let db;


    try {

        // Build the connection String and create the database connection
        const client = await MongoClient.connect(
            `mongodb://${process.env.DB_HOST}/${process.env.DB_NAME}`,
            {
                useNewUrlParser: true
            }
        )
        // db global variable 
        db = await Client.db(process.env.DB_NAME)
   
    }
    catch (err) {
        return console.log('Database Connection Error!', err.message)
    }
    
    return db;
}