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ActionController::Responder

Responsible for exposing a resource to different mime requests, usually depending on the HTTP verb. The responder is triggered when respond_with is called. The simplest case to study is a GET request:

  class PeopleController < ApplicationController
    respond_to :html, :xml, :json

    def index
      @people = Person.all
      respond_with(@people)
    end
  end

When a request comes in, for example for an XML response, three steps happen:

  1) the responder searches for a template at people/index.xml;

  2) if the template is not available, it will invoke <code>#to_xml</code> on the given resource;

  3) if the responder does not <code>respond_to :to_xml</code>, call <code>#to_format</code> on it.

Builtin HTTP verb semantics

The default Rails responder holds semantics for each HTTP verb. Depending on the content type, verb and the resource status, it will behave differently.

Using Rails default responder, a POST request for creating an object could be written as:

  def create
    @user = User.new(params[:user])
    flash[:notice] = 'User was successfully created.' if @user.save
    respond_with(@user)
  end

Which is exactly the same as:

  def create
    @user = User.new(params[:user])

    respond_to do |format|
      if @user.save
        flash[:notice] = 'User was successfully created.'
        format.html { redirect_to(@user) }
        format.xml { render :xml => @user, :status => :created, :location => @user }
      else
        format.html { render :action => "new" }
        format.xml { render :xml => @user.errors, :status => :unprocessable_entity }
      end
    end
  end

The same happens for PUT and DELETE requests.

Nested resources

You can supply nested resources as you do in form_for and polymorphic_url. Consider the project has many tasks example. The create action for TasksController would be like:

  def create
    @project = Project.find(params[:project_id])
    @task = @project.comments.build(params[:task])
    flash[:notice] = 'Task was successfully created.' if @task.save
    respond_with(@project, @task)
  end

Giving several resources ensures that the responder will redirect to project_task_url instead of task_url.

Namespaced and singleton resources require a symbol to be given, as in polymorphic urls. If a project has one manager which has many tasks, it should be invoked as:

  respond_with(@project, :manager, @task)

Note that if you give an array, it will be treated as a collection, so the following is not equivalent:

  respond_with [@project, :manager, @task]

Custom options

respond_with also allows you to pass options that are forwarded to the underlying render call. Those options are only applied for success scenarios. For instance, you can do the following in the create method above:

  def create
    @project = Project.find(params[:project_id])
    @task = @project.comments.build(params[:task])
    flash[:notice] = 'Task was successfully created.' if @task.save
    respond_with(@project, @task, :status => 201)
  end

This will return status 201 if the task was saved successfully. If not, it will simply ignore the given options and return status 422 and the resource errors. To customize the failure scenario, you can pass a a block to respond_with:

  def create
    @project = Project.find(params[:project_id])
    @task = @project.comments.build(params[:task])
    respond_with(@project, @task, :status => 201) do |format|
      if @task.save
        flash[:notice] = 'Task was successfully created.'
      else
        format.html { render "some_special_template" }
      end
    end
  end

Using respond_with with a block follows the same syntax as respond_to.

Constants

ACTIONS_FOR_VERBS

Attributes

controller[R]
request[R]
format[R]
resource[R]
resources[R]
options[R]

Public Class Methods

call(*args) click to toggle source

Initializes a new responder an invoke the proper format. If the format is not defined, call to_format.

     # File lib/action_controller/metal/responder.rb, line 145
145:     def self.call(*args)
146:       new(*args).respond
147:     end
new(controller, resources, options={}) click to toggle source
     # File lib/action_controller/metal/responder.rb, line 124
124:     def initialize(controller, resources, options={})
125:       @controller = controller
126:       @request = @controller.request
127:       @format = @controller.formats.first
128:       @resource = resources.last
129:       @resources = resources
130:       @options = options
131:       @action = options.delete(:action)
132:       @default_response = options.delete(:default_response)
133:     end

Public Instance Methods

respond() click to toggle source

Main entry point for responder responsible to dispatch to the proper format.

     # File lib/action_controller/metal/responder.rb, line 151
151:     def respond
152:       method = "to_#{format}"
153:       respond_to?(method) ? send(method) : to_format
154:     end
to_format() click to toggle source

All other formats follow the procedure below. First we try to render a template, if the template is not available, we verify if the resource responds to :to_format and display it.

     # File lib/action_controller/metal/responder.rb, line 174
174:     def to_format
175:       if get? || !has_errors? || response_overridden?
176:         default_render
177:       else
178:         display_errors
179:       end
180:     rescue ActionView::MissingTemplate => e
181:       api_behavior(e)
182:     end
to_html() click to toggle source

HTML format does not render the resource, it always attempt to render a template.

     # File lib/action_controller/metal/responder.rb, line 159
159:     def to_html
160:       default_render
161:     rescue ActionView::MissingTemplate => e
162:       navigation_behavior(e)
163:     end
to_js() click to toggle source

to_js simply tries to render a template. If no template is found, raises the error.

     # File lib/action_controller/metal/responder.rb, line 166
166:     def to_js
167:       default_render
168:     end

Protected Instance Methods

api_behavior(error) click to toggle source

This is the common behavior for formats associated with APIs, such as :xml and :json.

     # File lib/action_controller/metal/responder.rb, line 198
198:     def api_behavior(error)
199:       raise error unless resourceful?
200: 
201:       if get?
202:         display resource
203:       elsif post?
204:         display resource, :status => :created, :location => api_location
205:       else
206:         head :no_content
207:       end
208:     end
api_location() click to toggle source
Alias for: resource_location
default_action() click to toggle source

By default, render the :edit action for HTML requests with failure, unless the verb is POST.

     # File lib/action_controller/metal/responder.rb, line 270
270:     def default_action
271:       @action ||= ACTIONS_FOR_VERBS[request.request_method_symbol]
272:     end
default_render() click to toggle source

If a response block was given, use it, otherwise call render on controller.

     # File lib/action_controller/metal/responder.rb, line 228
228:     def default_render
229:       if @default_response
230:         @default_response.call(options)
231:       else
232:         controller.default_render(options)
233:       end
234:     end
display(resource, given_options={}) click to toggle source

Display is just a shortcut to render a resource with the current format.

  display @user, :status => :ok

For XML requests it’s equivalent to:

  render :xml => @user, :status => :ok

Options sent by the user are also used:

  respond_with(@user, :status => :created)
  display(@user, :status => :ok)

Results in:

  render :xml => @user, :status => :created
     # File lib/action_controller/metal/responder.rb, line 253
253:     def display(resource, given_options={})
254:       controller.render given_options.merge!(options).merge!(format => resource)
255:     end
display_errors() click to toggle source
     # File lib/action_controller/metal/responder.rb, line 257
257:     def display_errors
258:       controller.render format => resource_errors, :status => :unprocessable_entity
259:     end
has_errors?() click to toggle source

Check whether the resource has errors.

     # File lib/action_controller/metal/responder.rb, line 263
263:     def has_errors?
264:       resource.respond_to?(:errors) && !resource.errors.empty?
265:     end
json_resource_errors() click to toggle source
     # File lib/action_controller/metal/responder.rb, line 278
278:     def json_resource_errors
279:       {:errors => resource.errors}
280:     end
resource_errors() click to toggle source
     # File lib/action_controller/metal/responder.rb, line 274
274:     def resource_errors
275:       respond_to?("#{format}_resource_errors", true) ? send("#{format}_resource_errors") : resource.errors
276:     end
resource_location() click to toggle source

Returns the resource location by retrieving it from the options or returning the resources array.

     # File lib/action_controller/metal/responder.rb, line 219
219:     def resource_location
220:       options[:location] || resources
221:     end
Also aliased as: navigation_location, api_location
resourceful?() click to toggle source

Checks whether the resource responds to the current format or not.

     # File lib/action_controller/metal/responder.rb, line 212
212:     def resourceful?
213:       resource.respond_to?("to_#{format}")
214:     end
response_overridden?() click to toggle source
     # File lib/action_controller/metal/responder.rb, line 282
282:     def response_overridden?
283:       @default_response.present?
284:     end

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