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December 20, 2015 15:39
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An express.js application that uses async.js to initialize a MongoDB database connection pool before the application starts listening for HTTP requests. The database connection pool is shared using an application-wide variable named 'mongodb'.
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| var async = require('async'), | |
| MongoClient = require('mongodb').MongoClient, | |
| express = require('express'); | |
| var MONGODB_URL = 'mongodb://<username>:<password>@<host>:<port>/<database>', | |
| PORT = -1; | |
| async.waterfall([ | |
| function(cb) { | |
| MongoClient.connect(MONGODB_URL, function(err, db) { | |
| if (err) { | |
| return cb(err); | |
| } else { | |
| console.log("Connected to MongoDB"); | |
| cb(null, db); | |
| } | |
| }); | |
| }, | |
| function(db, cb) { | |
| try { | |
| app = express(); | |
| app.set('mongodb', db); | |
| // Simple inline example of using the connection. | |
| // You should use async or similar here as well | |
| // (kriskowal/q is also popular) instead | |
| // of nesting callbacks, and creating "callback hell". | |
| app.get('/users/:userId', function(req, res, next) { | |
| var db = req.app.get('mongodb'), | |
| userId = req.params['userId']; | |
| db.collection('users').findOne({'_id': userId}, function(err, userDoc) { | |
| if (err) { | |
| res.send(500); | |
| } | |
| if (!userDoc) { | |
| res.send(404); | |
| } else { | |
| res.send(userDoc); | |
| } | |
| }); | |
| }); | |
| app.listen(PORT); | |
| cb(); | |
| } catch (err) { | |
| cb(err); | |
| } | |
| } | |
| ], | |
| function(err, results) { | |
| if (err) { | |
| console.error(err.message); | |
| } else { | |
| console.log("App Started"); | |
| } | |
| }); |
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