How to reuse MongoClient object in Express 4.0 router middleware? - node.js

Question

In Express 3.x , I was able to reuse a single MongoClient object for the entire application.
app.js
var routes = require('./routes'); // Routes for our application
MongoClient.connect('mongodb://localhost:27017/blog', function(err, db) {
"use strict";
if(err) throw err;
app.engine('html', cons.swig);
app.set('view engine', 'html');
app.set('views', __dirname + '/views');
app.use(express.cookieParser());
app.use(express.bodyParser());
// Application routes
routes(app, db);
app.listen(8082);
console.log('Express server listening on port 8082');
});
routes/index.js
module.exports = exports = function(app, db) {
//do something
}
In express 4.0 , they introduced router middlewares.something like this
var routes = require('./routes/index');
app.use('/', routes);
how can i pass MOngoClient object to router middleware?

Answer 1

You could use separate module like 'Mongo.js' where you define your connection and store your MongoClient instance(_db).
Then include that module in your start up script specified (eg bin/www by default) and create a connection.
This way the connection will only be opened once, but you can also reuse the database object (_db) in your routes just by including 'Mongo.js'

Answer 2

You can still use the same pattern by modifying the routes/index.js
var express = require('express');
var router = express.Router();
module.exports = function(db) {
/* GET home page. */
router.get('/', function(req, res, next) {
res.render('index', { title: 'Express' });
});
return router;
}
Note the return router at the end.
And in your app.js:
MongoClient.connect('mongodb://localhost:27017/blog', function(err, db) {
...
app.use('/', routes(db))
...
}

Answer 3

Basically by creating a class that handles all your database actions, it reduces clutter in your app code. Plus, usage of callbacks allows you to effectively work with outputs you normally get in usual mongodb actions.
The sample code below clears all records in a sample collection named "records", effectively throws an error to the callback (if any), and also throws the results to the callback for you to work with.
Use the usual CRUD methods from the mongodb website as you like
# http://mongodb.github.io/node-mongodb-native/2.2/tutorials/crud/
Check the code below.
class SimpleMongoManager {
constructor(dbURL) {
if (!dbURL) {
console.error(`dbURL required!`);
throw (`# constructor`);
}
this.mongoClient = require('mongodb').MongoClient;
this.assert = require('assert');
this.dbURL = dbURL;
this.collectionName = collectionName;
}
initialize(callback) {
var self = this;
this.mongoClient.connect(this.dbURL, function(err, db) {
if (err) {
console.error(err);
throw (`# initialize # connect`);
} else {
self.db = db;
if (callback) {
callback(db);
}
}
});
}
gracefulExit() {
var self = this;
if (self.db) {
self.db.close();
}
}
debugClearRecords(callback){
var self = this;
self.db.collection("records").deleteMany({}, function(err, result) {
if(err){
console.error(err);
throw("# debugClearRecords # deleteMany");
}else{
if(callback){
callback(null, result.deletedCount);
}
}
});
}
}
/* Sample Usage */
var smInstance = new SimpleMongoManager("mongodb://localhost:27017/anterior");
smInstance.initialize(function(db){
console.log("DB Connection OK!");
});
smInstance.debugClearRecords(function(err, result){
console.log(err);
console.log(result);
});
/* Sample Route */
app.get('/clear_records', function(req, res){
/* Any checks here, if user is admin, whatever. */
smInstance.debugClearRecords(function(err, result){
console.log(err);
console.log(result);
res.redirect('/');
});
});