rails--rails/actionpack

= 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[http://activerecord.rubyonrails.org] (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[http://www.instiki.org], which is based on an older version
of Action Pack, used Madeleine for example). Read more about the role Action
Pack can play when used together with Active Record on
http://www.rubyonrails.org.

A short rundown of the major features:

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

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

  {Learn more}[link: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}[link: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

  {Learn more}[link:classes/ActionView/Base.html]


* 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 index
        # 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
        # exists, and the action will be logged for auditing.
        
        # After this action has run, the output will first be localized then 
        # compressed to minimize bandwidth usage
      end
      
      private
        def authenticate
          # Implement the filter with full access to both request and response
        end
    end
  
  {Learn more}[link: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}[link:classes/ActionView/Helpers.html]


* Layout sharing for template reuse (think simple version of Struts 
  Tiles[http://jakarta.apache.org/struts/userGuide/dev_tiles.html])

    class WeblogController < ActionController::Base
      layout "weblog_layout"
      
      def hello_world
      end
    end

    Layout file (called weblog_layout):
      <html><body><%= yield %></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}[link:classes/ActionController/Layout/ClassMethods.html]


* Routing makes pretty urls incredibly easy

    map.connect 'clients/:client_name/:project_name/:controller/:action'

    Accessing /clients/37signals/basecamp/project/dash calls ProjectController#dash with
    { "client_name" => "37signals", "project_name" => "basecamp" } in params[:params]
    
    From that URL, you can rewrite the redirect in a number of ways:
    
    redirect_to(:action => "edit") =>
      /clients/37signals/basecamp/project/dash

    redirect_to(:client_name => "nextangle", :project_name => "rails") =>
      /clients/nextangle/rails/project/dash

  {Learn more}[link:classes/ActionController/Base.html]


* Javascript and Ajax integration

    link_to_function "Greeting", "alert('Hello world!')"
    link_to_remote "Delete this post", :update => "posts", 
                   :url => { :action => "destroy", :id => post.id }
  
  {Learn more}[link:classes/ActionView/Helpers/JavaScriptHelper.html]


* Pagination for navigating lists of results

    # controller
    def list
      @pages, @people =
        paginate :people, :order => 'last_name, first_name'
    end

    # view
    <%= link_to "Previous page", { :page => @pages.current.previous } if @pages.current.previous %>
    <%= link_to "Next page", { :page => @pages.current.next } if @pages.current.next %>

  {Learn more}[link:classes/ActionController/Pagination.html]


* Easy testing of both controller and rendered template through ActionController::TestCase

    class LoginControllerTest < ActionController::TestCase
      def test_failing_authenticate
        process :authenticate, :user_name => "nop", :password => ""
        assert flash.has_key?(:alert)
        assert_redirected_to :action => "index"
      end
    end

  {Learn more}[link:classes/ActionController/TestCase.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")


* Caching at three levels of granularity (page, action, fragment)

    class WeblogController < ActionController::Base
      caches_page :show
      caches_action :account
      
      def show
        # the output of the method will be cached as 
        # ActionController::Base.page_cache_directory + "/weblog/show/n.html"
        # and the web server will pick it up without even hitting Rails
      end
      
      def account
        # the output of the method will be cached in the fragment store
        # but Rails is hit to retrieve it, so filters are run
      end
      
      def update
        List.update(params[:list][:id], params[:list])
        expire_page   :action => "show", :id => params[:list][:id]
        expire_action :action => "account"
        redirect_to   :action => "show", :id => params[:list][:id]
      end
    end

  {Learn more}[link:classes/ActionController/Caching.html]


* Component requests from one controller to another

    class WeblogController < ActionController::Base
      # Performs a method and then lets hello_world output its render
      def delegate_action
        do_other_stuff_before_hello_world
        render_component :controller => "greeter",  :action => "hello_world"
      end
    end
  
    class GreeterController < ActionController::Base
      def hello_world
        render_text "Hello World!"
      end
    end
  
    The same can be done in a view to do a partial rendering:
  
      Let's see a greeting:
      <%= render_component :controller => "greeter", :action => "hello_world" %>

  {Learn more}[link:classes/ActionController/Components.html]
  

* 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}[link:classes/ActionController/Rescue.html]


* Scaffolding for Active Record model objects

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

  {Learn more}[link:classes/ActionView/Helpers/ActiveRecordHelper.html]


* Runs on top of WEBrick, Mongrel, CGI, FCGI, and mod_ruby


== Simple example (from outside of Rails)

This example will implement a simple weblog system using inline templates and
an Active Record model. 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.view_paths = [ 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.erb:
    <html><body>
    <%= yield %>
    </body></html>

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

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

  weblog/new.erb:
    <%= 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 turn hands 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

Also note that these examples are all for demonstrating using Action Pack on
its own. Not for when it's used inside of Rails.

== Download

The latest version of Action Pack can be found at

* http://rubyforge.org/project/showfiles.php?group_id=249

Documentation can be found at 

* http://api.rubyonrails.com


== 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 MIT license.


== Support

The Action Pack homepage is http://www.rubyonrails.org. You can find
the Action Pack RubyForge page at http://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.