Action Controllers are the core of a web request in Rails. They are made up of one or more actions that are executed on request and then either render a template or redirect 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 Rails Routes.

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

Actions, by default, render a template in the app/views directory corresponding to the name of the controller and action after executing code in the action. For example, the index action of the GuestBookController would render the template app/views/guestbook/index.rhtml by default after populating the @entries instance variable.

Unlike index, the sign action will not render a template. After performing its main purpose (creating a new entry in the guest book), it 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.

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 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 server_ip
  location = request.env["SERVER_ADDR"]
  render :text => "This server hosted at #{location}"
end

Parameters

All request parameters, whether they come from a GET or POST request, or from the URL, are available through the params method which returns a hash. For example, 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[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 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 method, which accesses a hash:

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

And retrieved again through the same hash:

Hello #{session[:person]}

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.

By default, sessions are stored on the file system in RAILS_ROOT/tmp/sessions. 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 store on the filesystem. In other words, think carefully about size and caching before resorting to the use of the session on the filesystem.

An alternative to storing sessions on disk is to use ActiveRecordStore to store sessions in your database, which can solve problems caused by storing sessions in the file system and may speed up your application. To use ActiveRecordStore, uncomment the line:

config.action_controller.session_store = :active_record_store

in your environment.rb and run rake db:sessions:create.

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 and requires no user intervention.

Renders

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.

Redirects

Redirects are used to move from one action to another. For example, after a create action, which stores a blog entry to a database, we might like to show the user the new entry. Because we’re following good DRY principles (Don’t Repeat Yourself), we’re going to reuse (and redirect to) a show action that we’ll assume has already been created. The code might look like this:

def create
  @entry = Entry.new(params[:entry])
  if @entry.save
    # The entry was saved correctly, redirect to show
    redirect_to :action => 'show', :id => @entry.id
  else
    # things didn't go so well, do something else
  end
end

In this case, after saving our new entry to the database, the user is redirected to the show method which is then executed.

Calling multiple redirects or renders

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
Methods
C
D
E
F
H
I
P
R
S
U
Constants
DEFAULT_RENDER_STATUS_CODE = "200 OK"
 
DEPRECATED_INSTANCE_VARIABLES = %w(cookies flash headers params request response session)
 

TODO: assigns cookies headers params request response template
Attributes
[RW] action_name

Returns the name of the action this controller is processing.
[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.
Class Public methods
controller_class_name()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “NeatController”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 338
def controller_class_name
  @controller_class_name ||= name.demodulize
end
controller_name()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “neat”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 343
def controller_name
  @controller_name ||= controller_class_name.sub(%rController$/, '').underscore
end
controller_path()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “one_module/two_module/neat”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 348
def controller_path
  @controller_path ||= name.gsub(%rController$/, '').underscore
end
exempt_from_layout(*extensions)

Don’t render layouts for templates with the given extensions.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 414
def exempt_from_layout(*extensions)
  @@exempt_from_layout.merge extensions.collect { |extension|
    if extension.is_a?(Regexp)
      extension
    else
      %r\.#{Regexp.escape(extension.to_s)}$/
    end
  }
end
filter_parameter_logging(*filter_words, &block)

Replace sensitive paramater data from the request log. Filters paramaters that have any of the arguments as a substring. Looks in all subhashes of the param hash for keys to filter. If a block is given, each key and value of the paramater hash and all subhashes is passed to it, the value or key can be replaced using String#replace or similar method.

Examples:

filter_parameter_logging
=> Does nothing, just slows the logging process down

filter_parameter_logging :password
=> replaces the value to all keys matching %rpassword/ with "[FILTERED]"

filter_parameter_logging :foo, "bar"
=> replaces the value to all keys matching %rfoo|bar/ with "[FILTERED]"

filter_parameter_logging { |k,v| v.reverse! if k =~ %rsecret/ }
=> reverses the value to all keys matching %rsecret/

filter_parameter_logging(:foo, "bar") { |k,v| v.reverse! if k =~ %rsecret/ }
=> reverses the value to all keys matching %rsecret/, and
   replaces the value to all keys matching %rfoo|bar/ with "[FILTERED]"

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 388
def filter_parameter_logging(*filter_words, &block)
  parameter_filter = Regexp.new(filter_words.collect{ |s| s.to_s }.join('|'), true) if filter_words.length > 0

  define_method(:filter_parameters) do |unfiltered_parameters|
    filtered_parameters = {}

    unfiltered_parameters.each do |key, value|
      if key =~ parameter_filter
        filtered_parameters[key] = '[FILTERED]'
      elsif value.is_a?(Hash)
        filtered_parameters[key] = filter_parameters(value)
      elsif block_given?
        key = key.dup
        value = value.dup if value
        yield key, value
        filtered_parameters[key] = value
      else
        filtered_parameters[key] = value
      end
    end

    filtered_parameters
  end
end
hidden_actions()

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.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 355
def hidden_actions
  write_inheritable_attribute(:hidden_actions, ActionController::Base.public_instance_methods) unless read_inheritable_attribute(:hidden_actions)
  read_inheritable_attribute(:hidden_actions)
end
hide_action(*names)

Hide each of the given methods from being callable as actions.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 361
def hide_action(*names)
  write_inheritable_attribute(:hidden_actions, hidden_actions | names.collect { |n| n.to_s })
end
inherited(child)
Also aliased as: inherited_without_name_error

Source: show 

# File rails/actionwebservice/test/dispatcher_action_controller_soap_test.rb, line 8
def inherited(child)
  begin
    inherited_without_name_error(child)
  rescue NameError => e
  end
end
inherited_without_name_error(child)
process_cgi(cgi = CGI.new, session_options = {})

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:

  • :database_manager - standard options are CGI::Session::FileStore, CGI::Session::MemoryStore, and CGI::Session::PStore (default). Additionally, there is CGI::Session::DRbStore and CGI::Session::ActiveRecordStore. Read more about these in lib/action_controller/session.

  • :session_key - the parameter name used for the session id. Defaults to '_session_id'.

  • :session_id - the session id to use. If not provided, then it is retrieved from the session_key cookie, or automatically generated for a new session.

  • :new_session - if true, force creation of a new session. If not set, a new session is only created if none currently exists. If false, a new session is never created, and if none currently exists and the session_id option is not set, an ArgumentError is raised.

  • :session_expires - the time the current session expires, as a Time object. If not set, the session will continue indefinitely.

  • :session_domain - the hostname domain for which this session is valid. If not set, defaults to the hostname of the server.

  • :session_secure - if true, this session will only work over HTTPS.

  • :session_path - the path for which this session applies. Defaults to the directory of the CGI script.

  • :cookie_only - if true (the default), session IDs will only be accepted from cookies and not from the query string or POST parameters. This protects against session fixation attacks.

Source: show 

# File rails/actionpack/lib/action_controller/cgi_process.rb, line 29
def self.process_cgi(cgi = CGI.new, session_options = {})
  new.process_cgi(cgi, session_options)
end
process_test(request)

Process a test request called with a TestRequest object.

Source: show 

# File rails/actionpack/lib/action_controller/test_process.rb, line 6
def self.process_test(request)
  new.process_test(request)
end
Instance Public methods
controller_class_name()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “NeatController”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 532
def controller_class_name
  self.class.controller_class_name
end
controller_name()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “neat”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 537
def controller_name
  self.class.controller_name
end
controller_path()

Converts the class name from something like “OneModule::TwoModule::NeatController” to “one_module/two_module/neat”.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 542
def controller_path
  self.class.controller_path
end
process_with_test(*args)

Source: show 

# File rails/actionpack/lib/action_controller/test_process.rb, line 14
def process_with_test(*args)
  returning process_without_test(*args) do
    add_variables_to_assigns
  end
end
rescue_action(e)

Source: show 

# File rails/actionwebservice/test/abstract_dispatcher.rb, line 4
def rescue_action(e) raise e end
session_enabled?()

Test whether the session is enabled for this request.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 547
def session_enabled?
  request.session_options && request.session_options[:disabled] != false
end
url_for(options = {}, *parameters_for_method_reference)

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:

  • :anchor -- specifies the anchor name to be appended to the path. For example, url_for :controller => 'posts', :action => 'show', :id => 10, :anchor => 'comments' will produce "/posts/show/10#comments".

  • :only_path -- if true, returns the relative URL (omitting the protocol, host name, and port) (false by default)

  • :trailing_slash -- if true, adds a trailing slash, as in "/archive/2005/". Note that this is currently not recommended since it breaks caching.

  • :host -- overrides the default (current) host if provided

  • :protocol -- overrides the default (current) protocol if provided

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:

  • If the controller name begins with a slash, no defaults are used: url_for :controller => '/home'

  • If the controller changes, the action will default to index unless provided

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.

  • url_for :action => 'bio' -- During the generation of this URL, default values will be used for the first and

last components, and the action shall change. The generated URL will be, “people/hh/david/bio”.

  • url_for :first => 'davids-little-brother' This generates the URL 'people/hh/davids-little-brother' -- note that this URL leaves out the assumed action of '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.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 512
def url_for(options = {}, *parameters_for_method_reference) #:doc:
  case options
    when String
      options

    when Symbol
      ActiveSupport::Deprecation.warn(
        "You called url_for(:#{options}), which is a deprecated API call. Instead you should use the named " +
        "route directly, like #{options}(). Using symbols and parameters with url_for will be removed from Rails 2.0.",
        caller
      )

      send(options, *parameters_for_method_reference)

    when Hash
      @url.rewrite(rewrite_options(options))
  end
end
Instance Protected methods
default_url_options(options)

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.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 954
def default_url_options(options) #:doc:
end
expires_in(seconds, options = {})

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.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 1013
def expires_in(seconds, options = {}) #:doc:
  cache_options = { 'max-age' => seconds, 'private' => true }.symbolize_keys.merge!(options.symbolize_keys)
  cache_options.delete_if { |k,v| v.nil? or v == false }
  cache_control = cache_options.map{ |k,v| v == true ? k.to_s : "#{k.to_s}=#{v.to_s}"}
  response.headers["Cache-Control"] = cache_control.join(', ')
end
expires_now()

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).

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 1022
def expires_now #:doc:
  response.headers["Cache-Control"] = "no-cache"
end
head(*args)

Return a response that has no content (merely headers). The options argument is interpreted to be a hash of header names and values. This allows you to easily return a response that consists only of significant headers:

head :created, :location => person_path(@person)

It can also be used to return exceptional conditions:

return head(:method_not_allowed) unless request.post?
return head(:bad_request) unless valid_request?
render

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 885
def head(*args)
  if args.length > 2
    raise ArgumentError, "too many arguments to head"
  elsif args.empty?
    raise ArgumentError, "too few arguments to head"
  elsif args.length == 2
    status = args.shift
    options = args.shift
  elsif args.first.is_a?(Hash)
    options = args.first
  else
    status = args.first
    options = {}
  end

  raise ArgumentError, "head requires an options hash" if !options.is_a?(Hash)

  status = interpret_status(status || options.delete(:status) || :ok)

  options.each do |key, value|
    headers[key.to_s.dasherize.split(%r-/).map { |v| v.capitalize }.join("-")] = value.to_s
  end

  render :nothing => true, :status => status
end
redirect_to(options = {}, *parameters_for_method_reference)

Redirects the browser to the target specified in options. This parameter can take one of three forms:

  • Hash: The URL will be generated by calling #url_for with the options.

  • String starting with protocol:// (like http://): Is passed straight through as the target for redirection.

  • String not containing a protocol: The current protocol and host is prepended to the string.

  • :back: Back to the page that issued the request. Useful for forms that are triggered from multiple places. Short-hand for redirect_to(request.env)

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.

When using redirect_to :back, if there is no referrer, RedirectBackError will be raised. You may specify some fallback behavior for this case by rescueing RedirectBackError.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 976
def redirect_to(options = {}, *parameters_for_method_reference) #:doc:
  case options
    when %r{^\w+://.*}
      raise DoubleRenderError if performed?
      logger.info("Redirected to #{options}") if logger
      response.redirect(options)
      response.redirected_to = options
      @performed_redirect = true

    when String
      redirect_to(request.protocol + request.host_with_port + options)

    when :back
      request.env["HTTP_REFERER"] ? redirect_to(request.env["HTTP_REFERER"]) : raise(RedirectBackError)

    else
      if parameters_for_method_reference.empty?
        redirect_to(url_for(options))
        response.redirected_to = options
      else
        # TOOD: Deprecate me!
        redirect_to(url_for(options, *parameters_for_method_reference))
        response.redirected_to, response.redirected_to_method_params = options, parameters_for_method_reference
      end
  end
end
render(options = nil, deprecated_status = nil, &block)

Renders the content that will be returned to the browser as the response body.

Rendering an action

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).

Rendering partials

Partial rendering in a controller 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 same partial with a local variable.
render :partial => "person", :locals => { :name => "david" }

# Renders a collection of the same partial by making each element
# of @winners available through the local variable "person" as it
# builds the complete response.
render :partial => "person", :collection => @winners

# Renders the same collection of partials, but also renders the
# person_divider partial between each person partial.
render :partial => "person", :collection => @winners, :spacer_template => "person_divider"

# Renders a collection of partials located in a view subfolder
# outside of our current controller.  In this example we will be
# rendering app/views/shared/_note.r(html|xml)  Inside the partial
# each element of @new_notes is available as the local var "note".
render :partial => "shared/note", :collection => @new_notes

# Renders the partial with a status code of 500 (internal error).
render :partial => "broken", :status => 500

Note that the partial filename must also be a valid Ruby variable name, so e.g. 2005 and register-user are invalid.

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 = {}).

Rendering a template

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"

Rendering a file

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 text

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"

The :text option can also accept a Proc object, which can be used to manually control the page generation. This should generally be avoided, as it violates the separation between code and content, and because almost everything that can be done with this method can also be done more cleanly using one of the other rendering methods, most notably templates.

# Renders "Hello from code!"
render :text => proc { |response, output| output.write("Hello from code!") }

Deprecation notice: This used to have the signature render_text("text", status = 200)

Rendering JSON

Rendering JSON sets the content type to text/x-json and optionally wraps the JSON in a callback. It is expected that the response will be eval’d for use as a data structure.

# Renders '{name: "David"}'
render :json => {:name => "David"}.to_json

Sometimes the result isn’t handled directly by a script (such as when the request comes from a SCRIPT tag), so the callback option is provided for these cases.

# Renders 'show({name: "David"})'
render :json => {:name => "David"}.to_json, :callback => 'show'

Rendering an inline template

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)

Rendering inline JavaScriptGenerator page updates

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

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

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 713
def render(options = nil, deprecated_status = nil, &block) #:doc:
  raise DoubleRenderError, "Can only render or redirect once per action" if performed?

  if options.nil?
    return render_file(default_template_name, deprecated_status, true)
  else
    # Backwards compatibility
    unless options.is_a?(Hash)
      if options == :update
        options = { :update => true }
      else
        ActiveSupport::Deprecation.warn(
          "You called render('#{options}'), which is a deprecated API call. Instead you use " +
          "render :file => #{options}. Calling render with just a string will be removed from Rails 2.0.",
          caller
        )

        return render_file(options, deprecated_status, true)
      end
    end
  end

  if content_type = options[:content_type]
    response.content_type = content_type.to_s
  end

  if text = options[:text]
    render_text(text, options[:status])

  else
    if file = options[:file]
      render_file(file, options[:status], options[:use_full_path], options[:locals] || {})

    elsif template = options[:template]
      render_file(template, options[:status], true)

    elsif inline = options[:inline]
      render_template(inline, options[:status], options[:type], options[:locals] || {})

    elsif action_name = options[:action]
      ActiveSupport::Deprecation.silence do
        render_action(action_name, options[:status], options[:layout])
      end

    elsif xml = options[:xml]
      render_xml(xml, options[:status])

    elsif json = options[:json]
      render_json(json, options[:callback], options[:status])

    elsif partial = options[:partial]
      partial = default_template_name if partial == true
      if collection = options[:collection]
        render_partial_collection(partial, collection, options[:spacer_template], options[:locals], options[:status])
      else
        render_partial(partial, ActionView::Base::ObjectWrapper.new(options[:object]), options[:locals], options[:status])
      end

    elsif options[:update]
      add_variables_to_assigns
      @template.send :evaluate_assigns

      generator = ActionView::Helpers::PrototypeHelper::JavaScriptGenerator.new(@template, &block)
      render_javascript(generator.to_s)

    elsif options[:nothing]
      # Safari doesn't pass the headers of the return if the response is zero length
      render_text(" ", options[:status])

    else
      render_file(default_template_name, options[:status], true)

    end
  end
end
render_to_string(options = nil, &block)

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.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 791
def render_to_string(options = nil, &block) #:doc:
  ActiveSupport::Deprecation.silence { render(options, &block) }
ensure
  erase_render_results
  forget_variables_added_to_assigns
  reset_variables_added_to_assigns
end
reset_session()

Resets the session by clearing out all the objects stored within and initializing a new session object.

Source: show 

# File rails/actionpack/lib/action_controller/base.rb, line 1027
def reset_session #:doc:
  request.reset_session
  @_session = request.session
  response.session = @_session
end