In this post we will show you how easy to add basic API feature to an existing Rails application using Grape. Grape built to complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily provide APIs. By using Grape, we cut those heavy lifting works while building an API feature such as multiple formats response, subdomain/prefix restriction, and versioning.

Installation

In your Gemfile, add this

gem 'grape', '~> 0.1.5'

then

$ bundle install

Usage

In this example, I want to add couple API service to an existing application called Journal. In Journal, user add entries they want to keep. The API will provide GET /api/entries which should return all entries and GET /api/entries/1 which should return entry with id=1. Create a file named api.rb di lib directory

#lib/api.rb
module Journal
  class API < Grape::API
    prefix 'api'
    resource 'entries' do
      get do
        Entry.all
      end

      get ':id' do
        Entry.find(params[:id])
      end
    end
  end
end

Grape APIs are Rack applications that are created by subclassing Grape::API. In Rails 3, you can easily mount any Rack application. Just add the following line to your config/routes.rb file

mount Journal::API => "/"

You will need to this following too at the top of config/routes.rb file

require 'api'

Check your configuration by running

$ rake middleware

You should see

...
run Journal::Application.routes

Restart your application and try out your new API service at /api/entries and /api/entries/1.