Action Pack – On rails from request to response

Action Pack splits the response to a web request into a controller part (performing the logic) and a view part (rendering a template). This two-step approach is known as an action, which will normally create, read, update, or delete (CRUD for short) some sort of model part (often backed by a database) before choosing either to render a template or redirecting to another action.

Action Pack implements these actions as public methods on Action Controllers and uses Action Views to implement the template rendering. Action Controllers are then responsible for handling all the actions relating to a certain part of an application. This grouping usually consists of actions for lists and for CRUDs revolving around a single (or a few) model objects. So ContactController would be responsible for listing contacts, creating, deleting, and updating contacts. A WeblogController could be responsible for both posts and comments.

Action View templates are written using embedded Ruby in tags mingled in with the HTML. To avoid cluttering the templates with code, a bunch of helper classes provide common behavior for forms, dates, and strings. And it’s easy to add specific helpers to keep the separation as the application evolves.

Note: Some of the features, such as scaffolding and form building, are tied to ActiveRecord (an object-relational mapping package), but that doesn’t mean that Action Pack depends on Active Record. Action Pack is an independent package that can be used with any sort of backend (Instiki, which is based on an older version of Action Pack, uses Madeleine for example). Read more about the role Action Pack can play when used together with Active Record on www.rubyonrails.org.

A short rundown of the major features:

• Actions grouped in controller as methods instead of separate command objects and can therefore helper share methods.

  BlogController < ActionController::Base
    def display
      @customer = find_customer
    end
  
    def update
      @customer = find_customer
      @customer.attributes = @params["customer"]
      @customer.save ? 
        redirect_to(:action => "display") : 
        render("customer/edit")
    end
  
    private
      def find_customer() Customer.find(@params["id"]) end
  end
  

  Learn more in classes/ActionController/Base.html

• Embedded Ruby for templates (no new “easy” template language)

  <% for post in @posts %>
    Title: <%= post.title %>
  <% end %>
  
  All post titles: <%= @post.collect{ |p| p.title }.join ", " %>
  
  <% unless @person.is_client? %>
    Not for clients to see...
  <% end %>
  

  Learn more in classes/ActionView.html

• Builder-based templates (great for XML content, like RSS)

  xml.rss(“version” => “2.0”) do

  xml.channel do
    xml.title(@feed_title)
    xml.link(@url)
    xml.description "Basecamp: Recent items"
    xml.language "en-us"
    xml.ttl "40"
  
    for item in @recent_items
      xml.item do
        xml.title(item_title(item))
        xml.description(item_description(item))
        xml.pubDate(item_pubDate(item))
        xml.guid(@recent_items.url(item))
        xml.link(@recent_items.url(item))
      end
    end
  end
  

  end

• Filters for pre and post processing of the response (as methods, procs, and classes)

  class WeblogController < ActionController::Base
    before_filter :authenticate, :cache, :audit
    after_filter { |c| c.response.body = GZip::compress(c.response.body) }
    after_filter LocalizeFilter
  
    def list
      # Before this action is run, the user will be authenticated, the cache
      # will be examined to see if a valid copy of the results already
      # exist, and the action will be logged for auditing.
  
      # After this action has run, the output will first be localized then 
      # compressed to minimize bandwith usage
    end
  
    private
      def authenticate
        # Implement the filter will full access to both request and response
      end
  end
  

  Learn more in classes/ActionController/Filters/ClassMethods.html

• Helpers for forms, dates, action links, and text

  <%= text_field "post", "title", "size" => 30 %>
  <%= html_date_select(Date.today) %>
  <%= link_to "New post", :controller => "post", :action => "new" %>
  <%= truncate(post.title, 25) %>
  

  Learn more in classes/ActionView/Helpers.html

• Layout sharing for template reuse (think simple version of Struts Tiles)

  class WeblogController < ActionController::Base
    layout "weblog_layout"
  
    def hello_world
    end
  end
  
  Layout file (called weblog_layout):
    <html><body><%= @content_for_layout %></body></html>
  
  Template for hello_world action:
    <h1>Hello world</h1>
  
  Result of running hello_world action:
    <html><body><h1>Hello world</h1></body></html>
  

  Learn more in classes/ActionController/Layout/ClassMethods.html

• Advanced redirection that makes pretty urls easy

  RewriteRule ^/library/books/([A-Z]+)([0-9]+)/([-_a-zA-Z0-9]+)$ \
    /books_controller.cgi?action=$3&type=$1&code=$2 [QSA] [L]
  
  Accessing /library/books/ISBN/0743536703/show calls BooksController#show
  
  From that URL, you can rewrite the redirect in a number of ways:
  
  redirect_to(:action => "edit") =>
    /library/books/ISBN/0743536703/edit
  
  redirect_to(:path_params => { "type" => "XTC", "code" => "12354345" }) =>
    /library/books/XTC/12354345/show
  
  redirect_to(:controller_prefix => "admin", :controller => "accounts") =>
    /admin/accounts/
  

  Learn more in classes/ActionController/Base.html

• Easy testing of both controller and template result through TestRequest/Response

  class LoginControllerTest < Test::Unit::TestCase
    def setup
      @controller = LoginController.new
      @request    = ActionController::TestRequest.new
      @response   = ActionController::TestResponse.new
    end
  
    def test_failing_authenticate
      process :authenticate, "user_name" => "nop", "password" => ""
      assert_flash_has 'alert'
      assert_redirected_to :action => "index"
    end
  end
  

  Learn more in classes/ActionController/TestRequest.html

• Automated benchmarking and integrated logging

  Processing WeblogController#index (for 127.0.0.1 at Fri May 28 00:41:55)
  Parameters: {"action"=>"index", "controller"=>"weblog"}
  Rendering weblog/index (200 OK)
  Completed in 0.029281 (34 reqs/sec)
  
  If Active Record is used as the model, you'll have the database debugging
  as well:
  
  Processing WeblogController#create (for 127.0.0.1 at Sat Jun 19 14:04:23)
  Params: {"controller"=>"weblog", "action"=>"create",  
           "post"=>{"title"=>"this is good"} }
  SQL (0.000627) INSERT INTO posts (title) VALUES('this is good')
  Redirected to http://test/weblog/display/5
  Completed in 0.221764 (4 reqs/sec) | DB: 0.059920 (27%)
  
  You specify a logger through a class method, such as:
  
  ActionController::Base.logger = Logger.new("Application Log")
  ActionController::Base.logger = Log4r::Logger.new("Application Log")
  

• Powerful debugging mechanism for local requests

  All exceptions raised on actions performed on the request of a local user
  will be presented with a tailored debugging screen that includes exception
  message, stack trace, request parameters, session contents, and the
  half-finished response.
  

  Learn more in classes/ActionController/Rescue.html

• Scaffolding for Action Record model objects

  require 'account' # must be an Active Record class
  class AccountController < ActionController::Base
    scaffold :account
  end
  
  The AccountController now has the full CRUD range of actions and default
  templates: list, show, destroy, new, create, edit, update
  

  Learn more in classes/ActionController/Scaffolding/ClassMethods.html

• Form building for Active Record model objects

  The post object has a title (varchar), content (text), and 
  written_on (date)
  
  <%= form "post" %>
  
  ...will generate something like (the selects will have more options of
  course):
  
  <form action="create" method="POST">
    <p>
      <b>Title:</b><br/> 
      <input type="text" name="post[title]" value="<%= @post.title %>" />
    </p>
    <p>
      <b>Content:</b><br/>
      <textarea name="post[content]"><%= @post.title %></textarea>
    </p>
    <p>
      <b>Written on:</b><br/>
      <select name='post[written_on(3i)]'><option>18</option></select>
      <select name='post[written_on(2i)]'><option value='7'>July</option></select>
      <select name='post[written_on(1i)]'><option>2004</option></select>
    </p>
  
    <input type="submit" value="Create">
  </form>
  
  This form generates a @params["post"] array that can be used directly in a save action:
  
  class WeblogController < ActionController::Base
    def save
      post = Post.create(@params["post"])
      redirect_to :action => "display", :path_params => { "id" => post.id }
    end
  end
  

  Learn more in classes/ActionView/Helpers/ActiveRecordHelper.html

• Automated mapping of URLs to controller/action pairs through Apache’s mod_rewrite

  Requesting /blog/display/5 will call BlogController#display and 
  make 5 available as an instance variable through @params["id"]
  

• Runs on top of CGI, FCGI, and mod_ruby

  See the address_book_controller example for all three forms
  

Simple example

This example will implement a simple weblog system using inline templates and an Active Record model. The first thing we need to do is setup an .htaccess to interpret pretty URLs into something the controller can use. Let’s use the simplest form for starters:

RewriteRule ^weblog/([-_a-zA-Z0-9]+)/([0-9]+)$ \
  /weblog_controller.cgi?action=$2&id=$3 [QSA]
RewriteRule ^weblog/([-_a-zA-Z0-9]+)$ \
  /weblog_controller.cgi?action=$2 [QSA]
RewriteRule ^weblog/$ \
  /weblog_controller.cgi?action=index [QSA]

Now we’ll be able to access URLs like weblog/display/5 and have WeblogController#display called with { “id” => 5 } in the @params array available for the action. So let’s build that WeblogController with just a few methods:

require 'action_controller'
require 'post'
class WeblogController < ActionController::Base
  layout "weblog/layout"

  def index
    @posts = Post.find_all
  end

  def display
    @post = Post.find(@params["id"])
  end

  def new
    @post = Post.new
  end

  def create
    @post = Post.create(@params["post"])
    redirect_to :action => "display", :id => @post.id
  end
end

WeblogController::Base.template_root = File.dirname(__FILE__)
WeblogController.process_cgi if $0 == __FILE__

The last two lines are responsible for telling ActionController where the template files are located and actually running the controller on a new request from the web-server (like to be Apache).

And the templates look like this:

weblog/layout.rhtml:
  <html><body>
  <%= @content_for_layout %>
  </body></html>

weblog/index.rhtml:
  <% for post in @posts %>
    <p><%= link_to(post.title, :action => "display", :id => post.id %></p>
  <% end %>

weblog/display.rhtml:
  <p>
    <b><%= post.title %></b><br/>
    <b><%= post.content %></b>
  </p>

weblog/new.rhtml:
  <%= form "post" %>

This simple setup will list all the posts in the system on the index page, which is called by accessing /weblog/. It uses the form builder for the Active Record model to make the new screen, which in turns hand everything over to the create action (that’s the default target for the form builder when given a new model). After creating the post, it’ll redirect to the display page using an URL such as /weblog/display/5 (where 5 is the id of the post.

Examples

Action Pack ships with three examples that all demonstrate an increasingly detailed view of the possibilities. First is blog_controller that is just a single file for the whole MVC (but still split into separate parts). Second is the debate_controller that uses separate template files and multiple screens. Third is the address_book_controller that uses the layout feature to separate template casing from content.

Please note that you might need to change the “shebang” line to #!/usr/local/env ruby, if your Ruby is not placed in /usr/local/bin/ruby

Download

The latest version of Action Pack can be found at

• rubyforge.org/project/showfiles.php?group_id=249

Documentation can be found at

• actionpack.rubyonrails.org

Installation

You can install Action Pack with the following command.

% [sudo] ruby install.rb

from its distribution directory.

License

Action Pack is released under the same license as Ruby.

Support

The Action Pack homepage is actionpack.rubyonrails.org. You can find the Action Pack RubyForge page at rubyforge.org/projects/actionpack. And as Jim from Rake says:

Feel free to submit commits or feature requests.  If you send a patch,
remember to update the corresponding unit tests.  If fact, I prefer
new feature to be submitted in the form of new unit tests.

For other information, feel free to ask on the ruby-talk mailing list (which is mirrored to comp.lang.ruby) or contact david@loudthinking.com.