Rails 3 Routing with Rack

7 February 2010

You probably all have heard that “Rails lets you route to Rack applications directly” and thought “Oh really?” well… bet you didn’t think it would be this simple.

Rails 3 really opens up a whole new world of pluggable awesomeness. This post expects you have already installed Rails 3 —prerelease, if not, follow the instructions in the Release Notes

The goal here is to make a Sinatra app run inside of Rails, taking routes it needs directly using the new Rails routing features.

Code is better at talking than me, so first make a new app:

$ rails app

Let rails do its thing. Then we want to make a simple Sinatra app, let’s make it marginally useful and have it hit Twitter.

Make a directory lib/twitter and in there make a new file called twitter_app.rb, inside of it put:

class TwitterApp < Sinatra::Base
  set :root, File.dirname(__FILE__)

  get '/twitter' do
    @user = 'raasdnil'
    t = Twitter::Search.new(@user).fetch
    @tweets = t.results
    erb :twitter


This is a basic Sinatra app, it first sets its root directory to be the directory of the current file (needed because using the Rails root will not work) and then responds to one url /twitter that uses the Twitter gem to do the heavy lifting on searching for all the tweets by some weirdo (me).

It then assigns all the tweets to an instance variable and renders the template twitter.erb.

We have to make this template, so create another folder lib/twitter/views and make a file in there called twitter.erb and put in the following:

<!DOCTYPE html>
<html lang="en">
    <title>Tweets mentioning <%= @user %></title>
  <style type="text/css" media="screen">
    div.tweet { border: 1px solid gray;
                height: 50px;
                width: 600px;
                padding: 5px;
                margin-bottom: 10px; }
    img.icon { float: left; padding-right: 10px; }
    div.text { font-family: verdana, sans-serif; }
    div.<%= @user %> { background: #F4F4FF; }
    <% @tweets.each do |tweet| %>
    <div class="tweet  <%= tweet.from_user %>" id="<%= tweet.id %>">
      <img class="icon" src="<%= tweet.profile_image_url %>" />
      <div class="text" >
        <%= tweet.text %>
    <% end %>

OK, our Sinatra app is ready to fire. Now hooking it up is simple.

First, we need to make sure we require the needed gems, so open up your Gemfile in Rails root and add the following:

## Bundle the gems you use:
gem "sinatra", "0.9.2"
gem "twitter", "0.8.3"

Then do a bundle check to make sure we have the gems we need:

$ bundle check
The Gemfile's dependencies are satisfied

All good (if that gave you an error, just run bundle install).

Now the final step is to wire up the Rails Router.

Open up config/routes.rb and add a require for your twitter app as well as a route to match '/twitter' and send to your Sinatra App, something like this:

require 'twitter/twitter_app'

RackTest::Application.routes.draw do |map|

  match '/twitter', :to => TwitterApp


And that’s it!

Fire up your Rails app with rails s as you normally would, and browse to and proove it to yourself… this stuff works.

Almost too simple.



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