Node.js how to

Here is how to loop/iterate through a map in visualforce :

I was getting the "No space left on device" error for pretty much anything i try to do on my linux machine. Even using tab to autocomplete a command!

In reality, there was tons of free space though.

The reason is that I have run out of memory or space elsewhere.

I tried to unmount the overflow partition using:

umount /tmp

Cross domain sessions come into picture when your client and server are on different domains.

The way a session works is, client sends a login request to the server, on successful login, server stores session variables (probably in a datastore) and sends response to the client with a set-cookie header. Client then makes subsequent requests to the server with the cookie information present in the login response.

When both client and server are on same domain, this process is taken care by default. To enable cross domain session support though, we will have to make few changes.

On an express.js (version 4.0) server, to enable cross domain session support,

app.use(function(req, res, next) { //to allow cross domain requests to send cookie information. res.header('Access-Control-Allow-Credentials', true); // origin can not be '*' when crendentials are enabled. so need to set it to the request origin res.header('Access-Control-Allow-Origin', req.headers.origin); // list of methods that are supported by the server res.header('Access-Control-Allow-Methods','OPTIONS,GET,PUT,POST,DELETE'); res.header('Access-Control-Allow-Headers', 'X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept'); next(); });

On the client side,

If you are making an Ajax call, set the 'xhrfields.withCredentials' to true

I use Vagrant for my development environment and I came across this issue when I wanted to connect to my database that is installed on the virtual box (created from vagrant) from the mysql workbench. It took me a few minutes to figure it out so I thought this would be helpful to people like me who are working with vagrant.

SSH into vagrant using 'vagrant ssh'

Run this command to make sure your root user has the required privileges. Make sure you don't do this  on a non-dev environment

mysql -u root -e "GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY '' WITH GRANT OPTION; FLUSH PRIVILEGES;"

In the workbench,

click on Connect to database

Select the connection method as Standard TCP/IP over SSH

SSH hostname : 127.0.0.1:2222

SSH username : vagrant

SSH password: No password by default. But you can add one by SSHing into vagrant and using the command Sudo passwd vagrant

SSH Key path: On ubuntu, it is ~/.vagrant.d/insecure_private_key

Mysql hostname: 127.0.0.1

Mysql Server: 3306

Mysql user: root

find query in mongodb by default does a case sensitive search. If the attributes in your database are not stored in a specific case and you want to perform a case insensitive search on those attributes, it can be done using $regex and $options keywords like this:

db.collection.find({key:{$regex:value, $options:'i'}});

Node.js is continuously under development and the latest version keeps updating from time to time. Many of us have installed node long time ago and would like to update it to the latest version to use few packages that are supported only by newer node versions. For instance, to use node-inspector, one must have node 0.8.1 or above installed.

One way of doing it is getting the latest image from nodejs.org and installing it. Turns out that there is an easier way. Follow these simple steps below to upgrade your node package.

Clear your npm cache (sudo npm cache clean -f)

Install 'n'. 'n' is a Node helper that we will use to upgrade our node version.

Upgrade to latest version (sudo n stable)

Given that Eclipse is a wonderful tool to work with, I wanted to set it up to work with Node.js applications. Nodeclipse is an eclipse plugin that you need to install to develop and debug your Node.js applications. 

Follow these simple steps below to have your Eclipse IDE up and ready to create Node.js applications.

Install Node.js and npm from Nodejs.org

Get your latest copy of Eclipse from http://www.eclipse.org/downloads/

Once you install eclipse, Visit the Marketplace from Help->Eclispe Market Place

I came across this scenario, where I had to query the db for each item in a collection. I had to spend some time to figure out how to do this. So, I'm posting my solution here.

Since, db querying is asynchronous in nodejs, apiece of code like this would fail.

for(i=0; i<arr.length; i++) { var result = db.collection.find({_id:'some_id'}); res.write(i+':'+JSON.stringify(result)+','); } res.end();

The result would simply return undefined here since this db.collection.find() is an asynchronous call.

So, to avoid this,

for(i=0; i<arr.length; i++) { db.collection.find({_id:arr[i].id}, function(err, result) { if(!err && result.length>0){ res.write(arr[i]+':'+JSON.stringify(result[0])+','); } }); } res.end();

This will definitely solve the async call issue. But, inside res.write(), I am trying to write arr[i]. From the point the db.collection.find() call has been made to the point the result has been returned by the call, the 'i' value would have changed. So,

arr.foreach(obj) { db.collection.find({_id:obj.id}, function(err, result) { if(!err && result.length>0){ res.write(obj+':'+JSON.stringify(result[0])+','); } }); } res.end();

There is another issue here. Immediately after the foreach loop is executed, there is a res.end() statement. At this point, If there are any pending async calls to the db, the res.write() will fail after res.end() is executed. So, I tweaked the code further more.

1. Installation

Download and Install node from here

Create a project folder and navigate to the folder from command line and execute commands npm install express and npm install jade to install express.js, jade.

2. Setting up Server

Create a file named app.js inside the project folder.

Edit your app.js,

var express = require("express"); var app = express(); app.configure(function() { //Your server listens on this port app.set('port', process.env.PORT || 3001); // Setting path for your Jade Views. app.set('views', __dirname + '/views'); // Set view engine as Jade app.set('view engine', 'jade'); //use router to route request app.use(app.router); //set the path for your static files app.use(express.static(path.join(__dirname, 'public'))); //Routing Requests app.get('index', function(req, res){ //handing the request localhost:3001/index is done here res.render('index', {name:'Rocky'}); }) });