Creating RESTful API using Grape and RABL in Rails 4

We can create a RESTful API using Grape and RABL in Rails4.

Step 1: Add this GEMS in your Gem file, And do Bundle install.
 gem 'grape'
 gem 'rabl-rails'
 gem 'grape-rabl'
 gem 'rack-cors', :require => 'rack/cors'

Step 2: Create a file under lib directory called api.rb, and create a folder inside the view named as api.
# lib/api/v1/root.rb class API < Grape::API
end

Step 3: Add this line to your application.rb file
   config.paths.add "app/api", glob: "**/*.rb"
    config.autoload_paths += %W(#{config.root}/lib #{config.root}/app/api/*)

    config.middleware.use Rack::Cors do
      allow do
        origins '*'
        # location of your API
        resource '/*', :headers => :any, :methods => [:get, :post, :options, :put, :delete]
      end
    end

    config.middleware.use(Rack::Config) do |env|
      env['api.tilt.root'] = Rails.root.join "app", "views", "api"
    end

Step 4. Now a days every we have to send and json response. We will use rabl gem for it.Now we will modify our API a bit.

class API < Grape::API
  version 'v1', using: :header, vendor: "Application_name"
  format :json
  formatter :json, Grape::Formatter::Rabl
end

Step 5. Now we have to mount our api in the routes.

mount API => "/api", :at => '/'

Step 6. Now we can create a sample api
  desc "Sample Api"

  get '/all_users' , :rabl => 'all_users' do
     @users = User.all                                              

  end

Step 7. For the Api response we have to create a rabl file for this case all_users.rabl inside the app/api folder
Let say our user table has id, username and email then in the all_users.rabl file we will have to write.

object @users
attributes :id,
           :username,
           :email

Step 8. Now we can call the api from console.
curl http://localhost:3000/api/all_users

Step 9. Now we can add some basic http authentication if we want.
http_basic do |email, password| user = User.find_by_email(email) user && user.valid_password?(password) end
 
And we can call the api from the console.

curl http://localhost:3000/api/users/all_users -u "user:secret".

Step 10:  Create API which will accept parameter.
let just say we want to pass a parameter to our api like id

 get '/:id', :rabl => 'user' do
    @requests = User.where('id =?', params[:id]).first
end
Now call it like 

curl http://localhost:3000/api/users/10 -u "user:secret".

Step 11: You want to pass number of random parameter to a api then make the api call like this. Which may not be a REST approach but some times we need that.

  curl  "http://localhost:3000/api/users/get_user?dob=yyyy-mm-dd&id=10"

  get '/get_user', :rabl => 'user' do
    @requests = User.where('dob =? AND id =?', params[:dob], params[:id]).first
  end


So Finally our Api looks Like.

# lib/api/v1/root.rb
class API < Grape::API

  version 'v1', using: :header, vendor: "app_name"
  format :json
  formatter :json, Grape::Formatter::Rabl

  http_basic do |uname, password|
    user = User.find_by_username(uname)
    user && user.valid_password?(password)
  end

  helpers do

  end

  resource :users do
    get '/all_users' , :rabl => 'all_users' do
      @users = User.all
    end

    get '/:id', :rabl => 'user' do
      @requests = User.where('id =?', params[:id]).first
    end

    get '/get_user', :rabl => 'user' do
      @requests = User.where('dob =? AND id =?', params[:dob], params[:id]).first
    end
    
  end

end

I will discuss on rabl in my next blog post.

For all the gem documentation please check the below links.

https://github.com/intridea/grape
https://github.com/LTe/grape-rabl
https://github.com/ccocchi/rabl-rails