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module ActionController #:nodoc:
# Responder is responsible to expose a resource for 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.find(:all)
# respond_with(@people)
# end
# end
#
# When a request comes, for example with format :xml, three steps happen:
#
# 1) respond_with searches for a template at people/index.xml;
#
# 2) if the template is not available, it will create a responder, passing
# the controller and the resource and invoke :to_xml on it;
#
# 3) if the responder does not respond_to :to_xml, call to_format on it.
#
# === Builtin HTTP verb semantics
#
# Rails default 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 given nested resource 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 an array of resources, you ensure that the responder will redirect to
# project_task_url instead of task_url.
#
# Namespaced and singleton resources requires 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)
#
# Check polymorphic_url documentation for more examples.
#
class Responder
attr_reader :controller, :request, :format, :resource, :resources, :options
def initialize(controller, resources, options={})
@controller = controller
@request = controller.request
@format = controller.formats.first
@resource = resources.is_a?(Array) ? resources.last : resources
@resources = resources
@options = options
@default_response = options.delete(:default_response)
end
delegate :head, :render, :redirect_to, :to => :controller
delegate :get?, :post?, :put?, :delete?, :to => :request
# Undefine :to_json since it's defined on Object
undef_method(:to_json) if method_defined?(:to_json)
# Initializes a new responder an invoke the proper format. If the format is
# not defined, call to_format.
#
def self.call(*args)
responder = new(*args)
method = :"to_#{responder.format}"
responder.respond_to?(method) ? responder.send(method) : responder.to_format
end
# HTML format does not render the resource, it always attempt to render a
# template.
#
def to_html
default_render
rescue ActionView::MissingTemplate
if get?
raise
elsif has_errors?
render :action => default_action
else
redirect_to resource_location
end
end
# All others 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.
#
def to_format
default_render
rescue ActionView::MissingTemplate
raise unless resourceful?
if get?
display resource
elsif has_errors?
display resource.errors, :status => :unprocessable_entity
elsif post?
display resource, :status => :created, :location => resource_location
else
head :ok
end
end
protected
# Checks whether the resource responds to the current format or not.
#
def resourceful?
resource.respond_to?(:"to_#{format}")
end
# Returns the resource location by retrieving it from the options or
# returning the resources array.
#
def resource_location
options[:location] || resources
end
# If a given response block was given, use it, otherwise call render on
# controller.
#
def default_render
@default_response.call
end
# display is just a shortcut to render a resource with the current format.
#
# display @user, :status => :ok
#
# For xml request is 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
#
def display(resource, given_options={})
controller.render given_options.merge!(options).merge!(format => resource)
end
# Check if the resource has errors or not.
#
def has_errors?
resource.respond_to?(:errors) && !resource.errors.empty?
end
# By default, render the :edit action for html requests with failure, unless
# the verb is post.
#
def default_action
request.post? ? :new : :edit
end
end
end
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