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
When Action Pack is used inside of Rails, the template_root is automatically configured and you don’t need to call process_cgi yourself.
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 with the request accessor 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_IP"] render :text => "Hello stranger from #{location}" end
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 stemming 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 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 accessor:
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.
For removing objects from the session, you can either assign a single key to nil, like session[:person] = nil, or you can remove the entire session with reset_session.
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.
Action Controller 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 ERb templates. It’s automatically configured. 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 on 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 :action=> "no_results" when 1 then render :action=> "show" when 2..10 then render :action=> "show_many" end end
Read more about writing ERb and Builder templates in classes/ActionView/Base.html.
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 being 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 routes configuration file 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 "/clients/37signals/basecamp/project/dash" to somewhere else:
redirect_to(:action => "edit") => /clients/37signals/basecamp/project/dash redirect_to(:client_name => "nextangle", :project_name => "rails") => /clients/nextangle/rails/project/dash
Those redirects happen under the configuration of:
map.connect 'clients/:client_name/:project_name/:controller/:action'
An action should conclude with a single render or redirect. Attempting to try to do either again will result in a DoubleRenderError:
def do_something redirect_to :action => "elsewhere" render :action => "overthere" # raises DoubleRenderError end
If you need to redirect on the condition of something, then be sure to add "and return" to halt execution.
def do_something redirect_to(:action => "elsewhere") and return if monkeys.nil? render :action => "overthere" # won't be called unless monkeys is nil end
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) }
DEFAULT_RENDER_STATUS_CODE | = | "200 OK" |
process | -> | process_without_test |
action_name | [RW] | Returns the name of the action this controller is processing. |
assigns | [RW] | 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. |
headers | [RW] | 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. |
params | [RW] | 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. |
request | [RW] | Holds the request object that’s primarily used to get environment variables through access like request.env["REQUEST_URI"]. |
response | [RW] | 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_filters that wants to manipulate the output, such as a OutputCompressionFilter. |
session | [RW] | 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 or symbol. |
Converts the class name from something like "OneModule::TwoModule::NeatController" to "NeatController".
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 343 343: def controller_class_name 344: @controller_class_name ||= name.demodulize 345: end
Converts the class name from something like "OneModule::TwoModule::NeatController" to "neat".
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 348 348: def controller_name 349: @controller_name ||= controller_class_name.sub(/Controller$/, '').underscore 350: end
Converts the class name from something like "OneModule::TwoModule::NeatController" to "one_module/two_module/neat".
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 353 353: def controller_path 354: @controller_path ||= name.gsub(/Controller$/, '').underscore 355: end
Return an array containing the names of public methods that have been marked hidden from the action processor. By default, all methods defined in ActionController::Base and included modules are hidden. More methods can be hidden using hide_actions.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 360 360: def hidden_actions 361: write_inheritable_attribute(:hidden_actions, ActionController::Base.public_instance_methods) unless read_inheritable_attribute(:hidden_actions) 362: read_inheritable_attribute(:hidden_actions) 363: end
Hide each of the given methods from being callable as actions.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 366 366: def hide_action(*names) 367: write_inheritable_attribute(:hidden_actions, hidden_actions | names.collect { |n| n.to_s }) 368: end
Process a request extracted from an CGI object and return a response. Pass false as session_options to disable sessions (large performance increase if sessions are not needed). The session_options are the same as for CGI::Session:
# File vendor/rails/actionpack/lib/action_controller/cgi_process.rb, line 25 25: def self.process_cgi(cgi = CGI.new, session_options = {}) 26: new.process_cgi(cgi, session_options) 27: end
Process a test request called with a TestRequest object.
# File vendor/rails/actionpack/lib/action_controller/test_process.rb, line 7 7: def self.process_test(request) 8: new.process_test(request) 9: end
Converts the class name from something like "OneModule::TwoModule::NeatController" to "NeatController".
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 466 466: def controller_class_name 467: self.class.controller_class_name 468: end
Converts the class name from something like "OneModule::TwoModule::NeatController" to "neat".
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 471 471: def controller_name 472: self.class.controller_name 473: end
# File vendor/rails/actionpack/lib/action_controller/test_process.rb, line 15 15: def process_with_test(*args) 16: returning process_without_test(*args) do 17: add_variables_to_assigns 18: end 19: end
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 475 475: def session_enabled? 476: request.session_options[:disabled] != false 477: end
Returns a URL that has been rewritten according to the options hash and the defined Routes. (For doing a complete redirect, use redirect_to). url_for is used to: All keys given to url_for are forwarded to the Route module, save for the following:
The URL is generated from the remaining keys in the hash. A URL contains two key parts: the <base> and a query string. Routes composes a query string as the key/value pairs not included in the <base>.
The default Routes setup supports a typical Rails path of "controller/action/id" where action and id are optional, with action defaulting to ‘index’ when not given. Here are some typical url_for statements and their corresponding URLs:
url_for :controller => 'posts', :action => 'recent' # => 'proto://host.com/posts/recent' url_for :controller => 'posts', :action => 'index' # => 'proto://host.com/posts' url_for :controller => 'posts', :action => 'show', :id => 10 # => 'proto://host.com/posts/show/10'
When generating a new URL, missing values may be filled in from the current request’s parameters. For example, url_for :action => ‘some_action‘ will retain the current controller, as expected. This behavior extends to other parameters, including :controller, :id, and any other parameters that are placed into a Route’s path. The URL helpers such as url_for have a limited form of memory: when generating a new URL, they can look for missing values in the current request’s parameters. Routes attempts to guess when a value should and should not be taken from the defaults. There are a few simple rules on how this is performed:
The final rule is applied while the URL is being generated and is best illustrated by an example. Let us consider the route given by map.connect ‘people/:last/:first/:action’, :action => ‘bio’, :controller => ‘people’.
Suppose that the current URL is "people/hh/david/contacts". Let’s consider a few different cases of URLs which are generated from this page.
last components, and the action shall change. The generated URL will be, "people/hh/david/bio".
However, you might ask why the action from the current request, ‘contacts’, isn’t carried over into the new URL. The answer has to do with the order in which the parameters appear in the generated path. In a nutshell, since the value that appears in the slot for :first is not equal to default value for :first we stop using defaults. On it’s own, this rule can account for much of the typical Rails URL behavior. Although a convienence, defaults can occasionaly get in your way. In some cases a default persists longer than desired. The default may be cleared by adding :name => nil to url_for’s options. This is often required when writing form helpers, since the defaults in play may vary greatly depending upon where the helper is used from. The following line will redirect to PostController’s default action, regardless of the page it is displayed on:
url_for :controller => 'posts', :action => nil
If you explicitly want to create a URL that’s almost the same as the current URL, you can do so using the :overwrite_params options. Say for your posts you have different views for showing and printing them. Then, in the show view, you get the URL for the print view like this
url_for :overwrite_params => { :action => 'print' }
This takes the current URL as is and only exchanges the action. In contrast, url_for :action => ‘print’ would have slashed-off the path components after the changed action.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 457 457: def url_for(options = {}, *parameters_for_method_reference) #:doc: 458: case options 459: when String then options 460: when Symbol then send(options, *parameters_for_method_reference) 461: when Hash then @url.rewrite(rewrite_options(options)) 462: end 463: end
Overwrite to implement a number of default options that all url_for-based methods will use. The default options should come in the form of a hash, just like the one you would use for url_for directly. Example:
def default_url_options(options) { :project => @project.active? ? @project.url_name : "unknown" } end
As you can infer from the example, this is mostly useful for situations where you want to centralize dynamic decisions about the urls as they stem from the business domain. Please note that any individual url_for call can always override the defaults set by this method.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 788 788: def default_url_options(options) #:doc: 789: end
Sets a HTTP 1.1 Cache-Control header. Defaults to issuing a "private" instruction, so that intermediate caches shouldn’t cache the response.
Examples:
expires_in 20.minutes expires_in 3.hours, :private => false expires in 3.hours, 'max-stale' => 5.hours, :private => nil, :public => true
This method will overwrite an existing Cache-Control header. See www.w3.org/Protocols/rfc2616/rfc2616-sec14.html for more possibilities.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 842 842: def expires_in(seconds, options = {}) #:doc: 843: cache_options = { 'max-age' => seconds, 'private' => true }.symbolize_keys.merge!(options.symbolize_keys) 844: cache_options.delete_if { |k,v| v.nil? or v == false } 845: cache_control = cache_options.map{ |k,v| v == true ? k.to_s : "#{k.to_s}=#{v.to_s}"} 846: @response.headers["Cache-Control"] = cache_control.join(', ') 847: end
Sets a HTTP 1.1 Cache-Control header of "no-cache" so no caching should occur by the browser or intermediate caches (like caching proxy servers).
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 851 851: def expires_now #:doc: 852: @response.headers["Cache-Control"] = "no-cache" 853: end
Redirects the browser to the target specified in options. This parameter can take one of three forms:
Examples:
redirect_to :action => "show", :id => 5 redirect_to "http://www.rubyonrails.org" redirect_to "/images/screenshot.jpg" redirect_to :back
The redirection happens as a "302 Moved" header.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 806 806: def redirect_to(options = {}, *parameters_for_method_reference) #:doc: 807: case options 808: when %r{^\w+://.*} 809: raise DoubleRenderError if performed? 810: logger.info("Redirected to #{options}") if logger 811: response.redirect(options) 812: response.redirected_to = options 813: @performed_redirect = true 814: 815: when String 816: redirect_to(request.protocol + request.host_with_port + options) 817: 818: when :back 819: request.env["HTTP_REFERER"] ? redirect_to(request.env["HTTP_REFERER"]) : raise(RedirectBackError) 820: 821: else 822: if parameters_for_method_reference.empty? 823: redirect_to(url_for(options)) 824: response.redirected_to = options 825: else 826: redirect_to(url_for(options, *parameters_for_method_reference)) 827: response.redirected_to, response.redirected_to_method_params = options, parameters_for_method_reference 828: end 829: end 830: end
Renders the content that will be returned to the browser as the response body.
Action rendering is the most common form and the type used automatically by Action Controller when nothing else is specified. By default, actions are rendered within the current layout (if one exists).
# Renders the template for the action "goal" within the current controller render :action => "goal" # Renders the template for the action "short_goal" within the current controller, # but without the current active layout render :action => "short_goal", :layout => false # Renders the template for the action "long_goal" within the current controller, # but with a custom layout render :action => "long_goal", :layout => "spectacular"
Deprecation notice: This used to have the signatures render_action("action", status = 200), render_without_layout("controller/action", status = 200), and render_with_layout("controller/action", status = 200, layout).
Partial rendering is most commonly used together with Ajax calls that only update one or a few elements on a page without reloading. Rendering of partials from the controller makes it possible to use the same partial template in both the full-page rendering (by calling it from within the template) and when sub-page updates happen (from the controller action responding to Ajax calls). By default, the current layout is not used.
# Renders the partial located at app/views/controller/_win.r(html|xml) render :partial => "win" # Renders the partial with a status code of 500 (internal error) render :partial => "broken", :status => 500 # Renders the same partial but also makes a local variable available to it render :partial => "win", :locals => { :name => "david" } # Renders a collection of the same partial by making each element of @wins available through # the local variable "win" as it builds the complete response render :partial => "win", :collection => @wins # Renders the same collection of partials, but also renders the win_divider partial in between # each win partial. render :partial => "win", :collection => @wins, :spacer_template => "win_divider"
Deprecation notice: This used to have the signatures render_partial(partial_path = default_template_name, object = nil, local_assigns = {}) and render_partial_collection(partial_name, collection, partial_spacer_template = nil, local_assigns = {}).
Template rendering works just like action rendering except that it takes a path relative to the template root. The current layout is automatically applied.
# Renders the template located in [TEMPLATE_ROOT]/weblog/show.r(html|xml) (in Rails, app/views/weblog/show.rhtml) render :template => "weblog/show"
File rendering works just like action rendering except that it takes a filesystem path. By default, the path is assumed to be absolute, and the current layout is not applied.
# Renders the template located at the absolute filesystem path render :file => "/path/to/some/template.rhtml" render :file => "c:/path/to/some/template.rhtml" # Renders a template within the current layout, and with a 404 status code render :file => "/path/to/some/template.rhtml", :layout => true, :status => 404 render :file => "c:/path/to/some/template.rhtml", :layout => true, :status => 404 # Renders a template relative to the template root and chooses the proper file extension render :file => "some/template", :use_full_path => true
Deprecation notice: This used to have the signature render_file(path, status = 200)
Rendering of text is usually used for tests or for rendering prepared content, such as a cache. By default, text rendering is not done within the active layout.
# Renders the clear text "hello world" with status code 200 render :text => "hello world!" # Renders the clear text "Explosion!" with status code 500 render :text => "Explosion!", :status => 500 # Renders the clear text "Hi there!" within the current active layout (if one exists) render :text => "Explosion!", :layout => true # Renders the clear text "Hi there!" within the layout # placed in "app/views/layouts/special.r(html|xml)" render :text => "Explosion!", :layout => "special"
Deprecation notice: This used to have the signature render_text("text", status = 200)
Rendering of an inline template works as a cross between text and action rendering where the source for the template is supplied inline, like text, but its interpreted with ERb or Builder, like action. By default, ERb is used for rendering and the current layout is not used.
# Renders "hello, hello, hello, again" render :inline => "<%= 'hello, ' * 3 + 'again' %>" # Renders "<p>Good seeing you!</p>" using Builder render :inline => "xml.p { 'Good seeing you!' }", :type => :rxml # Renders "hello david" render :inline => "<%= 'hello ' + name %>", :locals => { :name => "david" }
Deprecation notice: This used to have the signature render_template(template, status = 200, type = :rhtml)
In addition to rendering JavaScriptGenerator page updates with Ajax in RJS templates (see ActionView::Base for details), you can also pass the :update parameter to render, along with a block, to render page updates inline.
render :update do |page| page.replace_html 'user_list', :partial => 'user', :collection => @users page.visual_effect :highlight, 'user_list' end
Rendering nothing is often convenient in combination with Ajax calls that perform their effect client-side or when you just want to communicate a status code. Due to a bug in Safari, nothing actually means a single space.
# Renders an empty response with status code 200 render :nothing => true # Renders an empty response with status code 401 (access denied) render :nothing => true, :status => 401
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 613 613: def render(options = nil, deprecated_status = nil, &block) #:doc: 614: raise DoubleRenderError, "Can only render or redirect once per action" if performed? 615: 616: # Backwards compatibility 617: unless options.is_a?(Hash) 618: if options == :update 619: options = {:update => true} 620: else 621: return render_file(options || default_template_name, deprecated_status, true) 622: end 623: end 624: 625: if content_type = options[:content_type] 626: headers["Content-Type"] = content_type 627: end 628: 629: if text = options[:text] 630: render_text(text, options[:status]) 631: 632: else 633: if file = options[:file] 634: render_file(file, options[:status], options[:use_full_path], options[:locals] || {}) 635: 636: elsif template = options[:template] 637: render_file(template, options[:status], true) 638: 639: elsif inline = options[:inline] 640: render_template(inline, options[:status], options[:type], options[:locals] || {}) 641: 642: elsif action_name = options[:action] 643: render_action(action_name, options[:status], options[:layout]) 644: 645: elsif xml = options[:xml] 646: render_xml(xml, options[:status]) 647: 648: elsif partial = options[:partial] 649: partial = default_template_name if partial == true 650: if collection = options[:collection] 651: render_partial_collection(partial, collection, options[:spacer_template], options[:locals], options[:status]) 652: else 653: render_partial(partial, ActionView::Base::ObjectWrapper.new(options[:object]), options[:locals], options[:status]) 654: end 655: 656: elsif options[:update] 657: add_variables_to_assigns 658: @template.send :evaluate_assigns 659: 660: generator = ActionView::Helpers::PrototypeHelper::JavaScriptGenerator.new(@template, &block) 661: render_javascript(generator.to_s) 662: 663: elsif options[:nothing] 664: # Safari doesn't pass the headers of the return if the response is zero length 665: render_text(" ", options[:status]) 666: 667: else 668: render_file(default_template_name, options[:status], true) 669: 670: end 671: end 672: end
Renders according to the same rules as render, but returns the result in a string instead of sending it as the response body to the browser.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 676 676: def render_to_string(options = nil, &block) #:doc: 677: result = render(options, &block) 678: 679: erase_render_results 680: forget_variables_added_to_assigns 681: reset_variables_added_to_assigns 682: 683: result 684: end
Resets the session by clearing out all the objects stored within and initializing a new session object.
# File vendor/rails/actionpack/lib/action_controller/base.rb, line 856 856: def reset_session #:doc: 857: @request.reset_session 858: @session = @request.session 859: @response.session = @session 860: end