[MongoDb][Node.js] Simple CRUD Demo against a Replica sets ( Raid-1, master-slaves cluster)

crud_replica_set.js

/**
 * Simple code to demonstrate CRUD function on a document against an replica set.
 * Run this command in this source code's directory to install required dependency: npm install mongodb
 */

var MongoClient = require('mongodb').MongoClient;
var assert = require('assert');

// Notice that the difference of connection string for connecting to a replica set and a single mongodb server,
var connection_string = "mongodb://127.0.0.1:27018, 127.0.0.1:27019, 127.0.0.1:27020/restaurant";

MongoClient.connect(connection_string, function(err, db){
	if (err) throw err;

	console.log("[INFO] - Connection to '"+connection_string+"' is established...");

	var menus = db.collection('menus');
	// Create a document & insert it into the database
	var new_document = {
		'name': 'Chicken Curry Rice',
		'price': 2.5
	};
	menus.insert(new_document, function(err, inserted){
		if (err) throw err;

		assert.ok(inserted != null);
		console.log('[INFO] - Successfully inserted '+ JSON.stringify(inserted)+' document into the database.');
		
		// Retrieve the created document 
		menus.findOne({'name': inserted[0].name }, function(err, doc){
			if (err) throw err;
			
			assert.notEqual(doc, null, 'findOne should return result');
			console.log('[INFO] - Retrieved document: '+JSON.stringify(doc));

			//  Update the created document
			var doc_id = doc._id;
			menus.update({_id: doc_id}, {'$set': {'price': 5.0}}, function(err, updatedDoc){
				if (err) throw err;

				console.log('[INFO] - Successfully updated '+updatedDoc+' document.');

				// Delete the created document
				menus.remove({_id:doc_id}, function(err, removedDoc){
					if (err) throw err;

					console.log('[INFO] - Successfully removed '+removedDoc+' document.');					

					console.log("[INFO] - Closing database connection ...");
					return db.close();
				});				
			});
		});
	});
});