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= Action Pack -- From request to response Action Pack is a framework for handling and responding to web requests. It provides mechanisms for *routing* (mapping request URLs to actions), defining *controllers* that implement actions, and generating responses by rendering *views*, which are templates of various formats. In short, Action Pack provides the view and controller layers in the MVC paradigm. It consists of several modules: * Action Dispatch, which parses information about the web request, handles routing as defined by the user, and does advanced processing related to HTTP such as MIME-type negotiation, decoding parameters in POST/PUT bodies, handling HTTP caching logic, cookies and sessions. * Action Controller, which provides a base controller class that can be subclassed to implement filters and actions to handle requests. The result of an action is typically content generated from views. * Action View, which handles view template lookup and rendering, and provides view helpers that assist when building HTML forms, Atom feeds and more. Template formats that Action View handles are ERB (embedded Ruby, typically used to inline short Ruby snippets inside HTML), and XML Builder. With the Ruby on Rails framework, users only directly interface with the Action Controller module. Necessary Action Dispatch functionality is activated by default and Action View rendering is implicitly triggered by Action Controller. However, these modules are designed to function on their own and can be used outside of Rails. A short rundown of some of the major features: * Actions grouped in controller as methods instead of separate command objects and can therefore share helper methods class CustomersController < ActionController::Base def show @customer = find_customer end def update @customer = find_customer if @customer.update_attributes(params[:customer]) redirect_to :action => "show" else render :action => "edit" end end private def find_customer Customer.find params[:id] end end {Learn more}[link:classes/ActionController/Base.html] * ERB templates (static content mixed with dynamic output from ruby) <% @posts.each do |post| %> Title: <%= post.title %> <% end %> All post titles: <%= @posts.collect{ |p| p.title }.join(", ") %> <% unless @person.is_client? %> Not for clients to see... <% end %> {Learn more}[link:classes/ActionView.html] * "Builder" 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" @recent_items.each do |item| 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 class WeblogController < ActionController::Base # filters as methods before_filter :authenticate, :cache, :audit # filter as a proc after_filter { |c| c.response.body = Gzip::compress(c.response.body) } # class filter 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_tag "post", "title", "size" => 30 %> <%= link_to "New post", :controller => "post", :action => "new" %> <%= truncate(post.title, :length => 25) %> {Learn more}[link:classes/ActionView/Helpers.html] * Layout sharing for template reuse 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 match 'clients/:client_name/:project_name/:controller/:action' Accessing "/clients/37signals/basecamp/project/index" calls ProjectController#index with { "client_name" => "37signals", "project_name" => "basecamp" } in `params` From that action, you can write the redirect in a number of ways: redirect_to(:action => "edit") => /clients/37signals/basecamp/project/edit redirect_to(:client_name => "nextangle", :project_name => "rails") => /clients/nextangle/rails/project/index {Learn more}[link:classes/ActionDispatch/Routing.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 Started GET "/weblog" for 127.0.0.1 at Fri May 28 00:41:55 Processing by WeblogController#index as HTML Rendered weblog/index.html.erb within layouts/application (25.7ms) Completed 200 OK in 29.3ms If Active Record is used as the model, you'll have the database debugging as well: Started POST "/posts" for 127.0.0.1 at Sat Jun 19 14:04:23 Processing by PostsController#create as HTML Parameters: {"post"=>{"title"=>"this is good"}} SQL (0.6ms) INSERT INTO posts (title) VALUES('this is good') Redirected to http://example.com/posts/5 Completed 302 Found in 221ms (Views: 215ms | ActiveRecord: 0.6ms) You specify a logger through a class method, such as: ActionController::Base.logger = ActiveSupport::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.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] * 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] == 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.all end def show @post = Post.find(params[:id]) end def new @post = Post.new end def create @post = Post.create(params[:post]) redirect_to :action => "show", :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 (e.g., Apache). And the templates look like this: weblog/layout.html.erb: <html><body> <%= yield %> </body></html> weblog/index.html.erb: <% @posts.each do |post| %> <p><%= link_to(post.title, :action => "show", :id => post.id) %></p> <% end %> weblog/show.html.erb: <p> <b><%= @post.title %></b><br/> <b><%= @post.content %></b> </p> weblog/new.html.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 show page using an URL such as /weblog/5 (where 5 is the id of the post). == Download and installation The latest version of Action Pack can be installed with RubyGems: % [sudo] gem install actionpack Source code can be downloaded as part of the Rails project on GitHub * https://github.com/rails/rails/tree/master/actionpack == License Action Pack is released under the MIT license: * http://www.opensource.org/licenses/MIT == Support API documentation is at * http://api.rubyonrails.org Bug reports and feature requests can be filed with the rest for the Ruby on Rails project here: * https://github.com/rails/rails/issues