Custom API Responder

gistfile1.rb

# app/models/api_v2_responder.rb
# This approach was heavily inspired by
# http://josephhsu.com/post/32746478033/rails-responders-api-versioning.
# Overriding the #to_json method wasn't right though, as it removed half of the
# awesome functionality of respond_with.
#
# @see https://github.com/rails/rails/blob/v3.2.17/actionpack/lib/action_controller/metal/responder.rb
class ApiV2Responder < ActionController::Responder
  # Override the original `#display` method to wrap the passed in resource in
  # the correspondingly named Presenter.
  def display(resource, given_options = {})
    controller.render given_options.merge!(options).merge!(format => present(resource))
  end

  private

  # Present the resource, or resources, if possible.
  def present(model_or_models)
    presenters = Array.wrap(model_or_models).map do |model|
      if (presenter = determine_presenter(model))
        presenter.new(model)
      else
        model
      end
    end

    # Ensure that an array of presenters is returned for :index pages, even if
    # only one presented resource exists.
    return presenters if options[:template] == "index" || presenters.many?
    presenters.first
  end

  # Try and find a correspondingly named presenter class for the passed in
  # resource.
  def determine_presenter(model)
    "Api::V2::#{model.class.name}Presenter".constantize
  rescue NameError
    nil
  end
end


# app/models/api_presenter_delegator.rb
# Facilitates the Presenter objects in use by the API.
#
# @see http://devblog.avdi.org/2012/01/31/decoration-is-best-except-when-it-isnt/
#   When to use Presenters
class ApiPresenterDelegator < SimpleDelegator
  # Redefine `#to_json` so that calling `#to_json` on a Presenter object will
  # call the presenter's version of `#as_json` instead of simply delegating to
  # the presented model's version of `as_json`.
  def to_json(*args)
    as_json.to_json(*args)
  end

  def presented?
    true
  end
end


# app/presenters/api/v2/foo_report_presenter.rb
module Api
  module V2
    class FooReportPresenter < ApiPresenterDelegator
      def as_json(options = {})
        {
          root_obj_name: {
            id: id,
            user: {
              id: user_id
            },
          }
        }.deep_merge(options)
      end
    end
  end
end