Class: ActionController::Base

Action Controllers are made up of one or more actions that performs its purpose and then either renders a template or redirects to another action. An action is defined as a public method on the controller, which will automatically be made accessible to the web-server through a mod_rewrite mapping. A sample controller could look like this:

  class GuestBookController < ActionController::Base
    def index
      @entries = Entry.find_all
    end

    def sign
      Entry.create(@params["entry"])
      redirect_to :action => "index"
    end
  end

  GuestBookController.template_root = "templates/"
  GuestBookController.process_cgi

All actions assume that you want to render a template matching the name of the action at the end of the performance unless you tell it otherwise. The index action complies with this assumption, so after populating the @entries instance variable, the GuestBookController will render "templates/guestbook/index.rhtml".

Unlike index, the sign action isn’t interested in rendering a template. So after performing its main purpose (creating a new entry in the guest book), it sheds the rendering assumption and initiates a redirect instead. This redirect works by returning an external "302 Moved" HTTP response that takes the user to the index action.

The index and sign represent the two basic action archetypes used in Action Controllers. Get-and-show and do-and-redirect. Most actions are variations of these themes.

Also note that it’s the final call to process_cgi that actually initiates the action performance. It will extract request and response objects from the CGI

Requests

Requests are processed by the Action Controller framework by extracting the value of the "action" key in the request parameters. This value should hold the name of the action to be performed. Once the action has been identified, the remaining request parameters, the session (if one is available), and the full request with all the http headers are made available to the action through instance variables. Then the action is performed.

The full request object is available in @request and is primarily used to query for http headers. These queries are made by accessing the environment hash, like this:

  def hello_ip
    location = @request.env["REMOTE_ADDRESS"]
    render_text "Hello stranger from #{location}"
  end

Parameters

All request parameters whether they come from a GET or POST request, or from the URL, are available through the @params hash. So an action that was performed through /weblog/list?category=All&limit=5 will include { "category" => "All", "limit" => 5 } in @params.

It’s also possible to construct multi-dimensional parameter hashes by specifying keys using brackets, such as:

  <input type="text" name="post[name]" value="david">
  <input type="text" name="post[address]" value="hyacintvej">

A request steeming from a form holding these inputs will include { "post" => { "name" => "david", "address" => "hyacintvej" }. If the address input had been named "post[address][street]", the @params would have included { "post" => { "address" => { "street" => "hyacintvej" } } }. There’s no limit to the depth of the nesting.

Sessions

Sessions allows you to store objects in memory between requests. This is useful for objects that are not yet ready to be persisted, such as a Signup object constructed in a multi-paged process, or objects that don’t change much and are needed all the time, such as a User object for a system that requires login. The session should not be used, however, as a cache for objects where it’s likely they could be changed unknowingly. It’s usually too much work to keep it all synchronized — something databases already excel at.

You can place objects in the session by using the @session hash:

  @session["person"] = Person.authenticate(user_name, password)

And retrieved again through the same hash:

  Hello #{@session["person"]}

Any object can be placed in the session (as long as it can be Marshalled). But remember that 1000 active sessions each storing a 50kb object could lead to a 50MB memory overhead. In other words, think carefully about size and caching before resorting to the use of the session.

Responses

Each action results in a response, which holds the headers and document to be sent to the user’s browser. The actual response object is generated automatically through the use of renders and redirects, so it’s normally nothing you’ll need to be concerned about.

Renders

Action Controllers sends content to the user by using one of five rendering methods. The most versatile and common is the rendering of a template. Included in the Action Pack is the Action View, which enables rendering of eRuby templates. It’s automatically configgured. The controller passes objects to the view by assigning instance variables:

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

Which are then automatically available to the view:

  Title: <%= @post.title %>

You don’t have to rely the automated rendering. Especially actions that could result in the rendering of different templates will use the manual rendering methods:

  def search
    @results = Search.find(@params["query"])
    case @results
      when 0 then render "weblog/no_results"
      when 1 then render_action "show"
      when 2..10 then render_action "show_many"
    end
  end

Read more about writing eRuby templates in classes/ActionView/ERbTemplate.html.

Redirects

Redirecting is what actions that update the model do when they’re done. The save_post method shouldn’t be responsible for also showing the post once it’s saved — that’s the job for show_post. So once save_post has completed its business, it’ll redirect to show_post. All redirects are external, which means that when the user refreshes his browser, it’s not going to save the post again, but rather just show it one more time.

This sounds fairly simple, but the redirection is complicated by the quest for a phenomenon known as "pretty urls". Instead of accepting the dreadful beings that is "weblog_controller?action=show&post_id=5", Action Controller goes out of its way to represent the former as "/weblog/show/5". And this is even the simple case. As an example of a more advanced pretty url consider "/library/books/ISBN/0743536703/show", which can be mapped to books_controller?action=show&type=ISBN&id=0743536703.

Redirects work by rewriting the URL of the current action. So if the show action was called by "/library/books/ISBN/0743536703/show", we can redirect to an edit action simply by doing redirect_to(:action => "edit"), which could throw the user to "/library/books/ISBN/0743536703/edit". Naturally, you’ll need to setup the .htaccess (or other mean of URL rewriting for the web server) to point to the proper controller and action in the first place, but once you have, it can be rewritten with ease.

Let’s consider a bunch of examples on how to go from "/library/books/ISBN/0743536703/edit" to somewhere else:

  redirect_to(:action => "show", :action_prefix => "XTC/123") =>
    "http://www.singlefile.com/library/books/XTC/123/show"

  redirect_to(:path_params => {"type" => "EXBC"}) =>
    "http://www.singlefile.com/library/books/EXBC/0743536703/show"

  redirect_to(:controller => "settings") =>
    "http://www.singlefile.com/library/settings/"

For more examples of redirecting options, have a look at the unit test in test/controller/url_test.rb. It’s very readable and will give you an excellent understanding of the different options and what they do.

Environments

Action Controller works out of the box with CGI, FastCGI, and mod_ruby. CGI and mod_ruby controllers are triggered just the same using:

  WeblogController.process_cgi

FastCGI controllers are triggered using:

  FCGI.each_cgi{ |cgi| WeblogController.process_cgi(cgi) }

Methods

action_methods
action_name
add_class_variables_to_assigns
add_instance_variables_to_assigns
add_template_helper
add_variables_to_assigns
assert_existance_of_template_file
assign_shortcuts
close_session
controller_class_name
controller_name
cookie
initialize_current_url
initialize_template_class
log_processing
perform_action
process_cgi
process_test
protected_instance_variables
redirect_to
redirect_to_path
redirect_to_url
render
render_action
render_file
render_template
render_text
request_origin
template_exists?
url_for

Included Modules

ClassInheritableAttributes

Constants

DEFAULT_RENDER_STATUS_CODE

"200 OK"

Attributes

[RW]	assigns	Holds the hash of variables that are passed on to the template class to be made available to the view. This hash is generated by taking a snapshot of all the instance variables in the current scope just before a template is rendered.
[RW]	cookies	Holds a hash of cookie names and values. Accessed like `@cookies["user_name"]` to get the value of the user_name cookie. This hash is read-only. You set new cookies using the cookie method.
[RW]	headers	Holds a hash of header names and values. Accessed like `@headers["Cache-Control"]` to get the value of the Cache-Control directive. Values should always be specified as strings.
[RW]	params	Holds a hash of all the GET, POST, and Url parameters passed to the action. Accessed like `@params["post_id"]` to get the post_id. No type casts are made, so all values are returned as strings.
[RW]	request	Holds the request object that’s primarily used to get environment variables through access like `@request.env["REQUEST_URI"]`.
[RW]	response	Holds the response object that’s primarily used to set additional HTTP headers through access like `@response.headers["Cache-Control"] = "no-cache"`. Can also be used to access the final body HTML after a template has been rendered through @response.body — useful for `after_filter`s that wants to manipulate the output, such as a OutputCompressionFilter.
[RW]	session	Holds a hash of objects in the session. Accessed like `@session["person"]` to get the object tied to the "person" key. The session will hold any type of object as values, but the key should be a string.

Public Class methods

add_template_helper(helper_module)

Makes all the (instance) methods in the helper module available to templates rendered through this controller. See ActionView::Helpers (classes/ActionView/Helpers.html) for more about making your own helper modules available to the templates.