Noupe Editorial Team June 24th, 2009

A Simple Twitter App with Ruby on Rails – Messages With Ajax

Ruby on Rails is a web application framework that promotes rapid development. Clients' demands are ever increasing yet they still expect the same quality of output. Frameworks, like Rails, help to achieve this; why?... here are some of the reasons:
  • Convention over Configuration (CoC):
    This is used to reduce the amount of up-front configuartion. The idea is; if you abide by certain coding conventions, you will have little, to none, configuration to do.
  • Object-Relational Mapping (ORM):
    ORM reducing coupling to the database. This abstraction allows you changed the DBMS provider with little trouble.
  • Structured Code:
    The MVC pattern forces you to organise your code in a clean, structured way. This results in more maintainable code.
  • Plugins:
    Plugins save you from re-inventing the wheel every time you want to add functionality to your app. For instance, making you web app capable of performing searches can be easily added with the acts_as_ferret plugin. There are many more plugins!

Who is this Tutorial for?

This tutorial is for people who have learnt the basics of Rails and want to take things to the next level. This tutorial is not a beginners guide for getting started with Rails. If you are just starting out with Rails I suggest this article from Six Revisions.

What this Tutorial Covers

In the first part of this three part series, we cover setting up a simple message model, which will hold the messages posted. Further to this, we will learn how to post a message asynchronously, using AJAX.

View Demo of Twitter App with Ruby on Rails

Basic Application Design

Ok, so you've decided to create a "twitter" style micro-blog using Ruby on Rails. First, we need to think about our basic requirements and from this we can model our application. There are many ways that this can be done, but we will use a simple technique in which you jot down a few paragraphs about how and what the application is expected to do then highlight the nouns. So, lets try it. My web app should work in a similar way to twitter. Users should be able to register with the site and create short posts. Users should be able to follow other users. Each user should be able to see their own posts plus the users they are following. Note that I've been selective in what nouns I've highlighted. You only really need to take notice of the nouns which you feel will need to store data to the database. I know there is more to twitter than this, but lets leave it simple. As you can see the "nouns", which will need to store data to the database are "posts" and "users". So we require two models: In the first part of the tutorial, we are going to deal with posts only.
  • Post
  • User

Creating the Project Files

Before we do anything we need to create a project for our twitter web app.
  > rails twitter -d mysql
As you can see, I will be using MySQL as the DBMS, however, feel free to use whatever database you want. Open the database.yml file in the config folder and modify the password as required. An example is shown below.
  adapter: mysql
  encoding: utf8
  database: twittest_development
  pool: 5
  username: root
  password: yourpassword
  host: localhost
Now, create the database with the "rake" command.
  > rake db:create

Implementing the basic Message Model

So let's go right ahead and generate the "Post" model and migrate it.
  > ruby script/generate model post message:text
  > rake db:migrate


Now, let's create a controller for the post model.
  > ruby script/generate controller posts
We need to set up some methods for interacting with the model. Edit your "posts_controller.rb" file and add the following methods:
class PostsController < ApplicationController
  def index
    @posts = Post.all(:order => "created_at DESC")
    respond_to do |format|
  def create
    @post = Post.create(:message => params[:message])
    respond_to do |format|
        format.html { redirect_to posts_path }
        flash[:notice] = "Message failed to save."
        format.html { redirect_to posts_path }
We only need two methods, "index" and "create". The index method creates an instance variable containing all the posts in descending order. The create method is used to create a new post.


Let's create the "index" view. First, we'll create a partial for posts. Create a file called "_post.html.erb" in the views/posts folder and add the code below.
<p><b>Posted <%= time_ago_in_words(post.created_at) %> ago</b></p>
<p><%= post.message %></p>
The index view is now very simple. Create a file called "index.html.erb" in the views/posts folder and add the code below.
<%= render :partial => @posts %>

Create some Posts

Open a console session and create a few new messages, as shown below.
  > ruby script/console
  Loading development environment (Rails 2.3.2)
  >> Post.create!(:message => "My first post" )
  >> Post.create!(:message => "Post number two!" )

Create a Form for Posts

Obviously you're not going to get the user to use the console to create messages. So, our next task is to inject some functionality into our web app to allow the user to create messages. Twitter has an input box above the indexed messages, which is used for submitting a new message; We will keep our web app the same. First, we will create a partial for the form, then we will render that partial at the top of the index view. Create a file called "_message_form.html.erb" in the posts view folder and add the following code:
<% form_tag(:controller => "posts", :action => "create") do %>
  <%= label_tag(:message, "What are you doing?") %><br />
  <%= text_area_tag(:message, nil, :size => "44x6") %><br /> 
  <%= submit_tag("Update") %>
<% end %>
Now, we need to modify the index view to render this partial at the top. Open the index.html.erb file and modify the code as follows:
< %= render :partial => "message_form" %>
< %= render :partial => @posts %>
For this to work we need to make one last modification. Open the route.rb file and map a new "posts" resource, as shown below. (Note: the comments from this file have been removed).
ActionController::Routing::Routes.draw do |map|
  map.resources :posts
  map.connect ':controller/:action/:id'
  map.connect ':controller/:action/:id.:format'
This creates a few named routes. If you look back to the "create" method in the posts controller, you'll see that we make use of the posts_path named route; Defining the posts resource makes this named route available. So, lets fire up the web server and a see how things look.
  > ruby script/server
Now open a browser and go to http://localhost:3000/posts. You should see a screen, as shown below.

Adding some AJAX

AJAX allows you to make asynchronous requests to the server using JavaScript. We will make use of AJAX to make the posting a message a bit smoother. When the user clicks on the "Update" button, we want the message to update without refreshing the browser. We have a few things to do to add AJAX functionality. First, lets change the "create" method in the posts controller:
  def create
    @post = Post.create(:message => params[:message])
    respond_to do |format|
        format.html { redirect_to posts_path }
        flash[:notice] = "Message failed to save."
        format.html { redirect_to posts_path }
The only change here is the "format.js" code, allowing the create method to respond to JavaScript. Next, we need to create a posts layout file. In the views/layout folder create a file called "posts.html.erb" and add the following code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<html xmlns="" xml:lang="en" lang="en">
  <%= javascript_include_tag :all %>
  <div id="content">
    <%= yield %>	
The main purpose of this is to make use of the "javascript_include_tag" call, which includes the relevant JavaScript files for AJAX and some visual effects. Next, we need to make a small addition to the index view ("index.html.erb").
<%= render :partial => "message_form" %>
<div id="posts">
  <%= render :partial => @posts %>
As you can see all we have added is a div block surrounding the posts partial. This will be used later when we are specifying where the AJAX response should be placed. Nearly there! Now we will add a div_for block to our post partial ("_post.html.erb").
<% div_for post do %>
  <p><b>Posted <%= time_ago_in_words(post.created_at) %> ago</b></p>
  <p><%= post.message %></p>
<% end %>
Edit the "_message_form.html.erb" partial and change the form_tag call to form_remote_tag as show in the code extract below:
<% form_remote_tag(:controller => "posts", :action => "create") do %>
The div_for operation create a div block with a unique id, this is especially useful when looping through several records. Finally, we need to create the rjs template. To do this, create a file called "create.js.rjs" in the views/posts folder and add the following code.
page.insert_html :top, :posts, :partial => @post
page[@post].visual_effect :highlight
The first line specifies that a new post partial will be rendered at the top of the posts div when the asynchronous call responds. The second line specifies that a "highlight" visual effect will be applied to that block when it is rendered. That's it! Start you web server again, browse to http://localhost:3000/posts and give it a go.

Make it Look Pretty!

Image by pvproductions on Freepik

I've created a stylesheet, which we can use to make things look a bit more respectful. Create a file called layout.css in the public/stylesheets folder then add the following CSS code:
  font-family: tahoma, sans-serif;
  font-size: 18px;
  background-color: #4B7399;
  width: 100%;
  color: #ffffff;
  margin: 0;
  text-align: center;

  width: 800px;
  margin: 0 auto; 
  text-align: left;

  padding: 5px 20px 5px 20px;
  background-color: #ffffff;
  margin: 20px 0 20px 0;
  color: #000000;
Finally, you will need to add stylesheet_link_tag call to the posts.html.erb layout file. As per below, the call should be placed in the head tag.
  <%= javascript_include_tag :all %>
  <%= stylesheet_link_tag 'layout' %>
OK! It doesn't look that pretty, but it will do for our purposes.

Setting up a Home Page

To have the root URL (http://localhost:3000) direct the user towards your posts you will first need to delete the public/index.html file. Do this now. The second thing you need to do is set up a route in your configroutes.rb file. Open routes.rb in notepad and add a new line to the end using map.root, as shown below.
ActionController::Routing::Routes.draw do |map|
  map.resources :posts
  map.connect ':controller/:action/:id'
  map.connect ':controller/:action/:id.:format'
  map.root :controller => "posts"
For more on routes, try the Rails API Documentation Now if you browse to http://localhost:3000. The request will be routed to the posts controller.


This concludes the first part of the series. Depending on the popularity of this article, parts 2 and 3 will follow shortly.

What have we Learnt?

You've learnt how to carry out basic application design and how to use this design to work out what models are required. Further to this, you've learnt how to use the console to help with the development of your application. Finally, you used AJAX to perform asynchronous requests to the server.

Author: Phil McClure

Phil McClure is a Software Developer from Belfast, Northern Ireland. His main interests are software architecture, design patterns and how these can be applied to web development. Phil blogs at Therailworld. Follow him on Twitter.
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  1. Great. I’d like to see where this is heading. Cant wait for the other parts to show up here.
    I generally tend to write my own javascript (using jquery) and not use a lot of rjs but that’s just a preference. I am not going to comment no the ruby code just yet.

  2. Thanks a lot for this.. It was a quick way to reinforce a lot of things I learned.. Thanx Keep them coming. (One thing though.. your tags keep showing up everywhere.) I quickly re wrote my views in haml though.

  3. This is very well presented – I haven’t tried it because it will take me ages to set up ruby – but its written so clearly with nice little text boxes etc – brilliant man.

  4. Great tutorial… Simple and easy to follow. Looking forward to parts 2 and 3! (Seeing as how this was posted to the front page of Digg, I hope it’s popular enough to warrant a follow-up)

  5. Yeah, just a note about some of the code blocks. There are some unwanted “” and “” tags in these areas:

    map.resources :posts


    Just remove them, they shouldn’t be there. I’ll try to get Noura to remove them from the tutorial.

      1. Not having much luck here, trying to get a html tag into a comment… Let’s try again. Bold tags, as in:-


    1. Phil, I have fixed the code in the post now.
      Thanks a lot for creating such a useful tutorial. Looking forward for your next tutorial in this series :)

  6. I’ve tried to post this a few times now, but it keeps getting blocked. This is the correct URL for getting the source code for this tutorial:-


  7. Man I wish I had the time to learn RoR, seems like a really great technology that may overpass PHP one day. Still a great tutorial, thanks!

  8. Just what the world needs, another web based twitter client ;-). Very nice tutorial, IMHO a nice one to get your feet wet with RoR.

  9. this tutorial is really simple and straight to the heart of rails , i will be looking forward to parts 2 and 3 , keep up the good work , many thanks christine

  10. hi!!! what version of rails you are using? becouse it throws me some errors out

    for example this ->

    unexpected ‘:’, expecting ‘)’
    @posts = Post.find(:all :order => “created_at DESC”)


  11. Whats with this??

    NameError in PostsController#index

    uninitialized constant PostsController
    RAILS_ROOT: /Users/kenfoust/Projects/RubyProjects/twitter

    Application Trace | Framework Trace | Full Trace
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/dependencies.rb:443:in `load_missing_constant’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/dependencies.rb:80:in `const_missing_with_dependencies’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/dependencies.rb:92:in `const_missing’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/inflector.rb:372:in `const_get’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/inflector.rb:372:in `block in constantize’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/inflector.rb:371:in `each’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/inflector.rb:371:in `constantize’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/activesupport-2.3.3/lib/active_support/core_ext/string/inflections.rb:162:in `constantize’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/actionpack-2.3.3/lib/action_controller/routing/route_set.rb:440:in `recognize’
    /Users/kenfoust/.gem/ruby/1.9.1/gems/actionpack-2.3.3/lib/action_controller/routing/route_set.rb:433:in `call’

  12. Hook us up Noope, I know nothing about Ruby on Rails. Although I wish I did. Find us a tutorial on ROR but for absolute very beginners, that use a Mac! This looks nice but I have no idea how to implement it.

  13. I am getting this error after part 1 of this tutorial, i have double checked everything and followed everything to a tee…

    undefined local variable or method `post’ for #

    any ideas???

  14. Great tutorial. Followed it through and it worked 1st time!

    1 question. When it comes to validation through posts.rb, i add:
    validates_presence_of :message
    and within the view, I have

    the validation works, but i dont get a message. What have i misseD?


  15. Thanks Phil McClure for the lovely post. As i’m new in ROR, didn’t understand the following lines, wiuld be better if you explain more

    page.insert_html :top, :posts, :partial => @post
    page[@post].visual_effect :highlight


  16. great tutorial!! how can we get this div to aoto refresh? suppose a situation where multiple users are using this,if one user adds a message it should automatically be displayed in the browsers of other users. thanks in advance for your help.

  17. Great tutorial Phil, thank you a lot for nice explaining and also usage if sample images after code where most other tutorials lack.

  18. Showing posts/_message_form.html.erb where line #1 raised:

    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.[]

    Extracted source (around line #1):

    1: “posts”, :action => “create”) do %>
    3: “44×6”) %>

    Trace of template inclusion: /posts/index.html.erb

  19. Thanks Phil McClure for the lovely post. But when i open the posts page the following error will occur please let me know the problem and solution.

    Showing posts/_message_form.html.erb where line #1 raised:

    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.[]

    Extracted source (around line #1):

    1: “posts”, :action => “create”) do %>
    3: “44×6?) %>

    Trace of template inclusion: /posts/index.html.erb

  20. Now, we need to modify the index view to render this partial at the top. Open the index.html.erb file and modify the code as follows:

    is this meant to be something missing or really ???

  21. i’ve tried:

    “posts”, :action => “create”, :remote => true do %>

    that didn’t gives an error, but i also didn’t work :( (the site will be simply reloaded)

  22. I can’t seem to get the AJAX to work… I’m using Rails 3, so I’m aware of the fact that form_remote_tag is deprecated. Right now, I’m using the line “posts”, :action => “create”, :remote => true) do %> at the top of my _message_form.html.erb… and the app isn’t throwing any errors, but it’s also not Ajaxified. I saw the comments above that seemed to address the problem, but their code didn’t seem complete or at least didn’t make sense to me. Anyone have any thoughts?

  23. Hmm, how to make it works with Rails 3?
    I use rails 3 routes, but I guess some more depreciated stuff is used here. What do I have to do the other way, anybody knows?

  24. i m implementing in rails 3,
    during AJAX implementing,in rails 3
    “posts”, :action => “create”) do %>
    this tag not support so i keep old one that is, with :remote => true add .
    “posts”, :action => “create”, :remote => true) do %>

    is it write ?

  25. I’ve got this section of the app working with Rails 3 (and removed any deprecated code, so I am getting no warnings in the console at runtime).

    I seem to be having an issue with the ajax, however – there is no highlight when I create a new post, which presumably there should be, so I assume that the page is not ajaxified (it is too light a page to tell if it is doing a full page reload or just a section).

    Any ideas anyone?

  26. Hi,

    I got routing error when i used below routing with rails versino 3.0 and ruby versino 1.9

    # map.resources :posts
    # map.connect ‘:controller/:action/:id’
    # map.connect ‘:controller/:action/:id.:format’

    I converted them to
    1)resources :posts
    2) unable to get the equivalent of line 2 above in rails 3.0
    3) match ‘:controller(/:action(/:id(.:format)))’

    Please let me know the conversion text to be use for line 2 in rails 3.0 version

  27. Hey guys, when I change the following line in: _message_form.html.erb

    <% form_tag …
    <% form_remote_tag …

    I receive a traceback. Not sure why.

    The traceback is:

    NoMethodError in Posts#index

    Showing C:/Users/linx/twitter/app/views/posts/_message_form.html.erb where line #1 raised:

    undefined method `form_remote_tag' for #<#:0xb66e350>
    Extracted source (around line #1):

    1: “posts”, :action => “create”) do %>
    4: “44×6”) %>
    Trace of template inclusion: app/views/posts/index.html.erb

    Rails.root: C:/Users/linx/twitter

    Application Trace | Framework Trace | Full Trace
    app/views/posts/_message_form.html.erb:1:in `_app_views_posts__message_form_html_erb__27854131_95637984_1132246′
    app/views/posts/index.html.erb:1:in `_app_views_posts_index_html_erb___206319701_95643984_0′
    app/controllers/posts_controller.rb:4:in `index’

    Assistance would be appreciated =)

    1. @ Tres , The code here was written for an older version of ruby and the function form_remote_tag has been depreciated. Part 2 of this tutorial is figuring out the proper way to do it.

  28. Phil this was great, l personally can’t wait for the continuation of this, great job man. Rails is made easy with your explanation

  29. I really do appreciate the article, but Im using Rails 3.2, so i think i need some help with the _message_form.html and the routes config, because right now i can see the old post which was created at the console, but cant see the form so i can write and update

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