CODEWITHSUNDEEP
node.jsmongodbexpress
Alexander Dahlberg
Alexander Dahlberg

Reputation: 79

How could I make a global mongodb connection that I can access from other files

So I have this main server file index.js:

const express = require('express')
const app = express()

const route = require('./route')

app.use('/main', route)
app.listen(3000)

and then I have the route.js file:

const express = require('express')
const router = express.Router()

router.get('/', (req, res) => {
  res.send('Hello from main')
})

module.exports = router

As the title implies, how could I make a global mongodb connection so that I don't have to make a new connection to the database on every route?
Thanks!

Upvotes: 0

Views: 251

Answers (1)

Robert Moskal
Robert Moskal

Reputation: 22553

I'm surprised there is no answer on SO to this. The most common pattern is to initialize your database connection in a separate module and to import it in any file that needs it.

The below was taken from this longer article https://itnext.io/how-to-share-a-single-database-connection-in-a-node-js-express-js-app-fcad4cbcb1e and was written in callback style. I've updated it a little to be promise based below:

/* Callback Style */

const assert = require("assert");
const client = require("mongodb").MongoClient;
const config = require("../config");
let _db;
module.exports = {
    getDb,
    initDb
};

function initDb(callback) {
  if (_db) {
    console.warn("Trying to init DB again!");
    return callback(null, _db);
  }
  client.connect(config.db.connectionString, 
  config.db.connectionOptions, connected);
  function connected(err, db) {
    if (err) {
      return callback(err);
    }
    console.log("DB initialized - connected to: " + 
      config.db.connectionString.split("@")[1]);
    _db = db;
    return callback(null, _db);
  }
}

function getDb() {
  assert.ok(_db, "Db has not been initialized. Please called init first.");
  return _db;
}

 /******************************************************************/
//The client
const initDb = require("./db").initDb;
const getDb = require("./db").getDb;
const app = require("express")();
const port = 3001;
app.use("/", exampleRoute);
initDb(function (err) {
    app.listen(port, function (err) {
        if (err) {
            throw err; //
        }
        console.log("API Up and running on port " + port);
    });
);
function exampleRoute(req, res){
 const db = getDb();
 //Do things with your database connection
 res.json(results);
}

Here's a promise based version without semi-colons which is how I might do it for itself. These functions would all become candidates for reuse between projects.

const assert = require("assert")
const client = require("mongodb").MongoClient
const config = require("../config")
let _db
module.exports = {
    getDb,
    initDb
}

function initDb() {
  if (_db) {
    console.warn("Trying to init DB again!");
    return Promise.resolve(true)
  }
  return client.connect(config.db.connectionString, 
  config.db.connectionOptions)
}

function getDb() {
  assert.ok(_db, "Db has not been initialized. Please called init first.")
  return _db
}

//////////////////////


const {initDb, getDb} = require("./db")
const app = require("express")()
const port = 3001

app.use("/", exampleRoute)

initDb().
    then(_ =>bootServer(port))
    .catch(console.log)

function bootServer(port) {
    app.listen(port, function (err) {
        if (err) {
            Promise.reject(err)
        }
        console.log("API Up and running on port " + port)
        Promise.resolve()
    })   
}    

function exampleRoute(req, res){
 const db = getDb();
 //Do things with your database connection
 res.json(results);
}

Upvotes: 3

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