Ruby on Rails Facebook Application using Koala Gem

Here is a another Facebook application example (check the python example), but this time it is with Ruby on Rails using Koala gem. The great thing about Koala is how it is easy integrated and straight forward. Here are the steps from the very beginning:

1- Create a new Ruby on Rails project:

rails new rorApp

2- Delete ./public/index.html file as it is not needed.


3- In Gemfile add:

gem 'koala', '1.3.0'

4- In ./config/initializers folder, add a constants.rb file with the following data:

APP_ID= '123456789' # please change!
APP_SECRET= '1b2n3n5n6n7m8m9n9m0m' # please change!
SITE_URL = 'http://localhost:3000/' # please change!

Where APP_ID and APP_SECRET are the values you have from the Facebook application you create in the developers section, and the SITE_URL is the root URL of your application website ('http://localhost:3000/' if our case of testing locally)


5- In ./config/routes.rb, add the following routes:

root :to => 'home#index'

match '/index' => 'home#index'
match '/login' => 'home#login'

The first line makes calling the root of your application points to your index page.

6- In ./app/views folder, create a 'home' folder and inside it create a 'index.html.erb' with any content you want to show. It will only be available after user logs in.

7- In ./app/controller folder, create a 'home_controller.rb' file with the following content:

class HomeController < ApplicationController
            
    def index   
        if params[:code]
            # acknowledge code and get access token from FB
            session[:access_token] = session[:oauth].get_access_token(params[:code])
        end  

        # auth established, now do a graph call:
        @api = Koala::Facebook::API.new(session[:access_token])

        begin
            @user_profile = @api.get_object("me")
        rescue Exception=>ex
            puts ex.message
            #if user is not logged in and an exception is caught, redirect to the page where logging in is requested
            redirect_to '/login' and return
        end

        respond_to do |format|
         format.html {   }    
        end
    end
    
    #########################################################
    
    def login
        session[:oauth] = Koala::Facebook::OAuth.new(APP_ID, APP_SECRET, SITE_URL + '/')
        @auth_url =  session[:oauth].url_for_oauth_code(:permissions=>"read_stream publish_stream")  

        redirect_to @auth_url
    end
    
    #########################################################
end

The code explains itself, but here is a quick explanation: When the index page is called, the application looks for the access token for the current user in the cookies ('session[]'). If not found, it will redirect to the login page. The login handler will do the authentication headache for you with the extra permissions you want and passes the root URL as a call back so that Facebook will call it after authentication is done. Then when the index page is called one more time with an authentication code, it will be used to get the access token needed for any later requests.
So when the user opens the index page, he will notice some redirects and message boxes asking for allowing your application and for extra permissions then he is redirected to your index page.

8- Now you have your application ready. Just run 'bundle' from your terminal (make sure you are in the root folder of your application) to install Koala and then 'rails s' to start the web service.

bundle
rails s

9- Finally here are some Graph API calls that you may use to get profile data, friends list, post text/image and text to user's wall.

@api = Koala::Facebook::API.new(session[:access_token])
@user_profile = @api.get_object("me")
@friends = @api.get_connections(user_profile["id"], "friends")
@api.put_wall_post("hi")
@api.put_picture("http://www.example.com/image.png", {:message => "an image of mine!"})

You can learn more about Koala gem from this link: https://github.com/arsduo/koala