missing_record_handler.rb

module MissingRecordHandler
  extend ActiveSupport::Concern

  included do
    # Catch any RecordNotFound errors and route them appropriately
    # to the 404 handler.
    #
    # (see #record_not_found)
    # (see #render_404)
    rescue_from ActiveRecord::RecordNotFound, :with => :render_404
  end

  module InstanceMethods
    # Helper method to ensure the proper error is always raised.
    # This should be called when throwing a not found error instead
    # of invoking the error directly.
    #
    # @returns [ActiveRecord::RecordNotFound]
    # (see #render_404)
    def record_not_found
      raise ActiveRecord::RecordNotFound
    end

  private

    # Handles any ActiveRecord::RecordNotFound errors that may be thrown during
    # the request cycle. It will push an entry into the log file and render the
    # appropriate response based on the mime type of the request.
    #
    # @note ensure that if you ever invoke this method you return immediately to
    #   avoid a possible double render error.
    def render_404(exception=nil)
      logger.info "Rendering 404 with exception: #{exception.message}" if exception.present?

      respond_to do |format|
        format.html { render :file => "#{Rails.root}/public/404.html", :status => :not_found, :layout => false }
        format.json { render :text => 'Not Found', :status => :not_found }
        format.xml  { head :not_found }
        format.any  { head :not_found }
      end
    end
  end
end