= 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 = 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]
* 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
