edge badge
Namespace
Methods
R
Instance Public methods
respond_to(*mimes, &block)

Without web-service support, an action which collects the data for displaying a list of people might look something like this:

def index
  @people = Person.all
end

Here's the same action, with web-service support baked in:

def index
  @people = Person.all

  respond_to do |format|
    format.html
    format.xml { render xml: @people }
  end
end

What that says is, “if the client wants HTML in response to this action, just respond as we would have before, but if the client wants XML, return them the list of people in XML format.” (Rails determines the desired response format from the HTTP Accept header submitted by the client.)

Supposing you have an action that adds a new person, optionally creating their company (by name) if it does not already exist, without web-services, it might look like this:

def create
  @company = Company.find_or_create_by(name: params[:company][:name])
  @person  = @company.people.create(params[:person])

  redirect_to(person_list_url)
end

Here's the same action, with web-service support baked in:

def create
  company  = params[:person].delete(:company)
  @company = Company.find_or_create_by(name: company[:name])
  @person  = @company.people.create(params[:person])

  respond_to do |format|
    format.html { redirect_to(person_list_url) }
    format.js
    format.xml  { render xml: @person.to_xml(include: @company) }
  end
end

If the client wants HTML, we just redirect them back to the person list. If they want JavaScript, then it is an Ajax request and we render the JavaScript template associated with this action. Lastly, if the client wants XML, we render the created person as XML, but with a twist: we also include the person's company in the rendered XML, so you get something like this:

<person>
  <id>...</id>
  ...
  <company>
    <id>...</id>
    <name>...</name>
    ...
  </company>
</person>

Note, however, the extra bit at the top of that action:

company  = params[:person].delete(:company)
@company = Company.find_or_create_by(name: company[:name])

This is because the incoming XML document (if a web-service request is in process) can only contain a single root-node. So, we have to rearrange things so that the request looks like this (url-encoded):

person[name]=...&person[company][name]=...&...

And, like this (xml-encoded):

<person>
  <name>...</name>
  <company>
    <name>...</name>
  </company>
</person>

In other words, we make the request so that it operates on a single entity's person. Then, in the action, we extract the company data from the request, find or create the company, and then create the new person with the remaining data.

Note that you can define your own XML parameter parser which would allow you to describe multiple entities in a single request (i.e., by wrapping them all in a single root node), but if you just go with the flow and accept Rails' defaults, life will be much easier.

If you need to use a MIME type which isn't supported by default, you can register your own handlers in config/initializers/mime_types.rb as follows.

Mime::Type.register "image/jpg", :jpg

Respond to also allows you to specify a common block for different formats by using any:

def index
  @people = Person.all

  respond_to do |format|
    format.html
    format.any(:xml, :json) { render request.format.to_sym => @people }
  end
end

In the example above, if the format is xml, it will render:

render xml: @people

Or if the format is json:

render json: @people

Since this is a common pattern, you can use the class method #respond_to with the #respond_with method to have the same results:

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

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

Formats can have different variants.

The request variant is a specialization of the request format, like :tablet, :phone, or :desktop.

We often want to render different html/json/xml templates for phones, tablets, and desktop browsers. Variants make it easy.

You can set the variant in a before_action:

request.variant = :tablet if request.user_agent =~ /iPad/

Respond to variants in the action just like you respond to formats:

respond_to do |format|
  format.html do |variant|
    variant.tablet # renders app/views/projects/show.html+tablet.erb
    variant.phone { extra_setup; render ... }
    variant.none  { special_setup } # executed only if there is no variant set
  end
end

Provide separate templates for each format and variant:

app/views/projects/show.html.erb
app/views/projects/show.html+tablet.erb
app/views/projects/show.html+phone.erb

When you're not sharing any code within the format, you can simplify defining variants using the inline syntax:

respond_to do |format|
  format.js         { render "trash" }
  format.html.phone { redirect_to progress_path }
  format.html.none  { render "trash" }
end

Variants also support common `any`/`all` block that formats have.

It works for both inline:

respond_to do |format|
  format.html.any   { render text: "any"   }
  format.html.phone { render text: "phone" }
end

and block syntax:

respond_to do |format|
  format.html do |variant|
    variant.any(:tablet, :phablet){ render text: "any" }
    variant.phone { render text: "phone" }
  end
end

You can also set an array of variants:

request.variant = [:tablet, :phone]

which will work similarly to formats and MIME types negotiation. If there will be no :tablet variant declared, :phone variant will be picked:

respond_to do |format|
  format.html.none
  format.html.phone # this gets rendered
end

Be sure to check the documentation of respond_with and ActionController::MimeResponds.respond_to for more examples.

# File actionpack/lib/action_controller/metal/mime_responds.rb, line 253
def respond_to(*mimes, &block)
  raise ArgumentError, "respond_to takes either types or a block, never both" if mimes.any? && block_given?

  if collector = retrieve_collector_from_mimes(mimes, &block)
    response = collector.response
    response ? response.call : render({})
  end
end
respond_with(*resources, &block)

For a given controller action, #respond_with generates an appropriate response based on the mime-type requested by the client.

If the method is called with just a resource, as in this example -

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

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

then the mime-type of the response is typically selected based on the request's Accept header and the set of available formats declared by previous calls to the controller's class method respond_to. Alternatively the mime-type can be selected by explicitly setting request.format in the controller.

If an acceptable format is not identified, the application returns a '406 - not acceptable' status. Otherwise, the default response is to render a template named after the current action and the selected format, e.g. index.html.erb. If no template is available, the behavior depends on the selected format:

  • for an html response - if the request method is get, an exception is raised but for other requests such as post the response depends on whether the resource has any validation errors (i.e. assuming that an attempt has been made to save the resource, e.g. by a create action) -

    1. If there are no errors, i.e. the resource was saved successfully, the response redirect's to the resource i.e. its show action.

    2. If there are validation errors, the response renders a default action, which is :new for a post request or :edit for patch or put.

    Thus an example like this -

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

    is equivalent, in the absence of create.html.erb, to -

    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 }
        else
          format.html { render action: "new" }
          format.xml { render xml: @user }
        end
      end
    end
    
  • for a javascript request - if the template isn't found, an exception is raised.

  • for other requests - i.e. data formats such as xml, json, csv etc, if the resource passed to respond_with responds to to_<format>, the method attempts to render the resource in the requested format directly, e.g. for an xml request, the response is equivalent to calling render xml: resource.

Nested resources

As outlined above, the resources argument passed to respond_with can play two roles. It can be used to generate the redirect url for successful html requests (e.g. for create actions when no template exists), while for formats other than html and javascript it is the object that gets rendered, by being converted directly to the required format (again assuming no template exists).

For redirecting successful html requests, respond_with also supports the use of nested resources, which are supplied in the same way as in form_for and polymorphic_url. For example -

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

This would cause respond_with to redirect to project_task_url instead of task_url. For request formats other than html or javascript, if multiple resources are passed in this way, it is the last one specified that is rendered.

Customizing response behavior

Like respond_to, respond_with may also be called with a block that can be used to overwrite any of the default responses, e.g. -

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

  respond_with(@user) do |format|
    format.html { render }
  end
end

The argument passed to the block is an ActionController::MimeResponds::Collector object which stores the responses for the formats defined within the block. Note that formats with responses defined explicitly in this way do not have to first be declared using the class method respond_to.

Also, a hash passed to respond_with immediately after the specified resource(s) is interpreted as a set of options relevant to all formats. Any option accepted by render can be used, e.g.

respond_with @people, status: 200

However, note that these options are ignored after an unsuccessful attempt to save a resource, e.g. when automatically rendering :new after a post request.

Two additional options are relevant specifically to respond_with -

  1. :location - overwrites the default redirect location used after a successful html post request.

  2. :action - overwrites the default render action used after an unsuccessful html post request.

# File actionpack/lib/action_controller/metal/mime_responds.rb, line 390
def respond_with(*resources, &block)
  if self.class.mimes_for_respond_to.empty?
    raise "In order to use respond_with, first you need to declare the "            "formats your controller responds to in the class level."
  end

  if collector = retrieve_collector_from_mimes(&block)
    options = resources.size == 1 ? {} : resources.extract_options!
    options = options.clone
    options[:default_response] = collector.response
    (options.delete(:responder) || self.class.responder).call(self, resources, options)
  end
end