Facebook App by Rails using Koala

To get to know much about developing Facebook applications using a server side, I have chosen with Koala for Rails.  For .NET, Facebook C# SDK is being well supported by Microsoft also (http://facebooksdk.codeplex.com/).  In this post, I explain how to use Koala in your Rails applications.  As any Facebook app, the prerequisite  are:

  • Facebook account (of course you should be the one in the 10% of world population 🙂 )
  • A Facebook application (which could be in sandbox mode), so you should have App ID, App Secret and Callback URL
  • A Rails application in your local machine and the Facebook app pointed to this as http://localhost:3000 (default port for Mongrel or WEBrick)

Installing Koala

Install Koala gem from https://github.com/arsduo/koala by using sudo gem install koala –pre

Configuring Koala

Create facebook.yml in /config with the following content

# config/facebook.yml
 app_id: 184xxxxxxxxxxxx
 secret_key: 80xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 callback_url: http://localhost:3000/

Add the following in config/environment.rb

# config/environment.rb
# in Rails::Initializer.run do |config|
config.action_controller.allow_forgery_protection = false
config.gem "koala"

The first line enables Facebook callback to your server.  The following line adds koala gem into this application.

Create koala.rb in /config/initializers with the following content

# config/initializers/koala.rb

module Facebook
 CONFIG = YAML.load_file(Rails.root + "/config/facebook.yml")[Rails.env]
 APP_ID = CONFIG['app_id']
 SECRET = CONFIG['secret_key']
 CALLBACK_URL = CONFIG['callback_url']

Koala::Facebook::OAuth.class_eval do
 def initialize_with_default_settings(*args)
 case args.size
 when 0, 1
 raise "application id and/or secret are not specified in the config" unless Facebook::APP_ID && Facebook::SECRET
 initialize_without_default_settings(Facebook::APP_ID.to_s, Facebook::SECRET.to_s, Facebook::CALLBACK_URL.to_s)
 when 2, 3

 alias_method_chain :initialize, :default_settings

The above code loads the Facebook.yml settings into Facebook, so you can access AppID, AppSecret and CallbackURL anywhere in your application in an unified way.  The following OAuth extension method is taken from Koala guidance to simplify the instantiation of OAuth.new.

Controller Part

In ApplicationController, add the following


# protect_from_forgery

before_filter :parse_facebook_cookies
def parse_facebook_cookies
 @facebook_cookies = Koala::Facebook::OAuth.new.get_user_info_from_cookie(cookies)

Note that protect_from_forgery has been commented.  The following instructions, let this application load OAuth details from cookies for getting Facebook access token.

Your Login Page

Add the following on your login page layout, in this case /app/views/layout/login.html.erb

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"
 <meta http-equiv="content-type" content="text/html;charset=UTF-8" />
 <title>Udooz Sample</title>
 <script type="text/javascript" src="http://connect.facebook.net/en_US/all.js"></script>

<p style="color: green"><%= flash[:notice] %></p>
<div id="fb-root"></div>

<script type="text/javascript">
 appId  : '<%= Facebook::APP_ID %>',
 status : true, // check login status
 cookie : true, // enable cookies to allow the server to access the session
 xfbml  : true  // parse XFBML

 FB.login(function(response) {
 if (response.session) {
 location.href = '/home'
 } else {
 // user cancelled login

In this example, I’ve used Facebook JavaScript SDK for login screen.  To use this, I’ve include FBML scheme in <html> as xml:fb=”http://www.facebook.com/2008/fbml” followed by referring Facebook SDK script file.

You Home Page

In your home page, add the following things.

In app/controllers/HomeController.rb

class HomeController < ApplicationController
  def index
    graph = Koala::Facebook::GraphAPI.new(@facebook_cookies["access_token"])
    @likes = graph.get_connections("me", "likes")

In the above code, new Graph instance has been created.  By using this, I’ve invoked the currently logged in user’s likes.

In app/views/home.html.erb

<table border="0">
 <% if @likes %>
 <% for like in @likes %>
 <td><b><%=h like["name"]%> </b></td>
 <td><%=h like["category"] %></td>
 <% end %>
 <% end %>

Now, run your application.  Hope it would be easy.

15 thoughts on “Facebook App by Rails using Koala

  1. Hi,

    my /environment.rb is like this :

    # Load the rails application
    require File.expand_path(‘../application’, __FILE__)

    # Initialize the rails application

    config.action_controller.allow_forgery_protection = false
    config.gem “koala”

    and when I try to run my server, I got the following errors :

    => Booting WEBrick
    => Rails 3.0.4 application starting in development on
    => Call with -d to detach
    => Ctrl-C to shutdown server
    /usr/local/lib/ruby/1.9.1/syck.rb:145:in `initialize’: No such file or directory – /config/facebook.yml (Errno::ENOENT)
    from /usr/local/lib/ruby/1.9.1/syck.rb:145:in `open’
    from /usr/local/lib/ruby/1.9.1/syck.rb:145:in `load_file’
    from /home/nicolas/web/config/initializers/koala.rb:4:in `’
    from /home/nicolas/web/config/initializers/koala.rb:3:in `’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:235:in `load’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:235:in `block in load’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:225:in `block in load_dependency’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:596:in `new_constants_in’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:225:in `load_dependency’
    from /home/nicolas/web/devise/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:235:in `load’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/engine.rb:201:in `block (2 levels) in ‘
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/engine.rb:200:in `each’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/engine.rb:200:in `block in ‘
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/initializable.rb:25:in `instance_exec’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/initializable.rb:25:in `run’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/initializable.rb:50:in `block in run_initializers’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/initializable.rb:49:in `each’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/initializable.rb:49:in `run_initializers’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/application.rb:134:in `initialize!’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/application.rb:77:in `method_missing’
    from /home/nicolas/web/config/environment.rb:5:in `’
    from /home/nicolas/web/config.ru:3:in `require’
    from /home/nicolas/web/config.ru:3:in `block in ‘
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/builder.rb:46:in `instance_eval’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/builder.rb:46:in `initialize’
    from /home/nicolas/web/config.ru:1:in `new’
    from /home/nicolas/web/config.ru:1:in `’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/builder.rb:35:in `eval’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/builder.rb:35:in `parse_file’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/server.rb:162:in `app’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/server.rb:248:in `wrapped_app’
    from /home/nicolas/web/devise/gems/rack-1.2.2/lib/rack/server.rb:213:in `start’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/commands/server.rb:65:in `start’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/commands.rb:30:in `block in ‘
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/commands.rb:27:in `tap’
    from /home/nicolas/web/devise/gems/railties-3.0.4/lib/rails/commands.rb:27:in `’
    from script/rails:6:in `require’
    from script/rails:6:in `’

    It seems it does not recognize the config object in the environment.rb file.

    Thanks for your help,



    • CONFIG = YAML.load_file(Rails.root + “/config/facebook.yml”)[Rails.env]

      in this line got me a little further. now I have this error:
      ../initializers/koala.rb:6: syntax error, unexpected tCONSTANT, expecting ‘)’ (SyntaxError)
      FB_SECRET = CONFIG[‘secret_key’]

  2. I stumbled upon your blog on Google, and I’m glad to hear that you chose Koala to start experimenting with Facebook applications! If I may ask, what made you decide to use Koala over any other Facebook Ruby libraries?

    By the way, Koala is now officially on version 1.0 and the recommended way to install it is using “sudo gem install koala” (without the –pre option.)


  3. NoMethodError in HomeController#index

    You have a nil object when you didn’t expect it!
    You might have expected an instance of ActiveRecord::Base.
    The error occurred while evaluating nil.[]

    Application Trace | Framework Trace | Full Trace

    app/controllers/home_controller.rb:3:in `index’

  4. OAuthException: (#200) The user hasn’t authorized the application to perform this action

  5. If you wanted to Save some Information belonging to this logged in user. How would you do it?

    Whould the user model only contain the facebook id?
    and lets say some gamestats belong to this facebook id?

    • It varies based on your app nature:
      * use facebook id as one of your user ID and for the internal data store access, use respective database primary key ID.

  6. Pingback: Fetch data from facebook « My Blog

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