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Sample Ruby web-development tutorial

This is an example tutorial for teaching web development with Ruby.

Install Sinatra

gem install sinatra

Coach: Explain shortly what Sinatra is.

Create your first Sinatra app

Create a suffragist.rb file with the following contents:

require 'sinatra'

get '/' do
  'Hello, voter!'
end

Run your app

Go to the directory where you put your app and run ruby suffragist.rb. Now you can visit localhost:4567. You should see a ‘Hello, voter!’ page, which means that the generation of your new app worked correctly. Hit ctrl-c in the terminal to quit the server.

Coach: Explain POST and GET methods, and how to communicate with the browser.

Add the index view

To keep everything in order let’s make a directory for our views (and name it views).

Put this code into an index.erb file in the views directory:

<!DOCTYPE html>
<html>
  <head>
    <meta charset='UTF-8' />
    <title>Suffragist</title>
    <link href='//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css' rel='stylesheet' />
  </head>
  <body class='container'>
    <p>Cast your vote:</p>
    <form action='cast' method='post'>
      <ul class='unstyled'>
        <% Choices.each do |id, text| %>
          <li>
            <label class='radio'>
              <input type='radio' name='vote' value='<%= id %>' id='vote_<%= id %>' />
              <%= text %>
            </label>
          </li>
        <% end %>
      </ul>
      <button type='submit' class='btn btn-primary'>Cast this vote!</button>
    </form>
  </body>
</html>

And into suffragist.rb:

Choices = {
  'krk' => 'Cracow',
  'rad' => 'Radom',
  'waw' => 'Warsaw',
  'wro' => 'Wrocław',
}

Change the get action:

get '/' do
  erb :index
end

Run ruby suffragist.rb, check your results and quit the server with ctrl-c.

Coach: Talk a little about HTML. Explain templates. Explain what global costants are.

Templates

Adjust the index.erb file in the views directory and add the <h1>…</h1> line:

…
  <body class='container'>
    <h1><%= @title %></h1>
    <p>Cast your vote:</p>
…

Change the get action:

get '/' do
  @title = 'Welcome to the Suffragist!'
  erb :index
end

Coach: Explain what instance variables are and how Sinatra makes them visible in the views.

Add the ability to POST results

Put this into suffragist.rb:

post '/cast' do
  @title = 'Thanks for casting your vote!'
  @vote  = params['vote']
  erb :cast
end

Create a new file in the views directory, cast.erb, and put there some HTML with embedded Ruby code:

<!DOCTYPE html>
<html>
  <head>
    <meta charset='UTF-8' />
    <title>Suffragist</title>
    <link href='//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css' rel='stylesheet' />
  </head>
  <body class='container'>
    <h1><%= @title %></h1>
    <p>You cast: <%= Choices[@vote] %></p>
    <p><a href='/results'>See the results!</a></p>
  </body>
</html>

Coach: Explain how POST works. How to catch what was sent in the form? Where do params come from?

Factor out a common layout

Create layout.erb file in the views directory. Put the following in there:

<!DOCTYPE html>
<html>
  <head>
    <meta charset='UTF-8' />
    <title>Suffragist</title>
    <link href='//netdna.bootstrapcdn.com/twitter-bootstrap/2.3.1/css/bootstrap-combined.min.css' rel='stylesheet' />
  </head>
  <body class='container'>
    <h1><%= @title %></h1>
    <%= yield %>
  </body>
</html>

Remove the above parts from the other two templats (index.erb and cast.erb in the views directory).

Coach: Talk about the structure of HTML documents and how factoring out common code work in general. Explain what yield does.

Add the results route and the results view

Put this into suffragist.rb:

get '/results' do
  @votes = { 'waw' => 7, 'krk' => 5 }
  erb :results
end

Create a new file in the views directory, results.erb.

<table class='table table-hover table-striped'>
  <% Choices.each do |id, text| %>
    <tr>
      <th><%= text %></th>
      <td><%= @votes[id] || 0 %>
      <td><%= '#' * (@votes[id] || 0) %></td>
    </tr>
  <% end %>
</table>
<p><a href='/'>Cast more votes!</a></p>

Watch the page (run ruby suffragist.rb, check your results and quit the server with ctrl-c).

Coach: Explain HTML tables and how how the missing values from the hash default to zero.

Persist the results using YAML::Store

Time for something new! Let’s store our choices.

Add the following to the top of suffragist.rb:

require 'yaml/store'

Add some more code into suffragist.rb – replace post '/cast' and get '/results' with the following:

post '/cast' do
  @title = 'Thanks for casting your vote!'
  @vote  = params['vote']
  @store = YAML::Store.new 'votes.yml'
  @store.transaction do
    @store['votes'] ||= {}
    @store['votes'][@vote] ||= 0
    @store['votes'][@vote] += 1
  end
  erb :cast
end

get '/results' do
  @title = 'Results so far:'
  @store = YAML::Store.new 'votes.yml'
  @votes = @store.transaction { @store['votes'] }
  erb :results
end

Coach: Explain what YAML is.

See how the YAML file changes when votes are cast

Let’s open votes.yml. And vote. And check again.

Coach: There will be situations when one or more students will forget to quit the server before running it again. It’s a good opportunity to search the Internet for a solution. They don’t have to know everything about killing processes to find a solution.

Coach: In the end explain shortly the differences between Sinatra and Rails.

Play with the app

Try to change things in the app in any way you see fit:

  • Add some additional logic to the views.
  • Redirect to the results outright.
  • Add other votings; how would the YAML file need to change?
  • Try to style the file in different ways.