Setting up custom formats for respond_to and respond_with in Ruby on Rails 4

Question

I'm getting a ActionView::MissingTemplate when trying to get a custom output to behave with respond_to/with like it behaves xml/json output.

I have a custom output format available on my object.

@item.to_custom

I've registered the format with a custom Mime::Type registered in the mime_types.rb .

Mime::Type.register "application/custom", :custom

I have it listed in my respond_to options in my controller

class ItemsController < ApplicationController
  respond_to :html, :xml, :custom

And then I have a respond_with method before the end of my show action.

def show
  @item = Item.find(params[:id])    
  respond_with(@item) 
end

When I access items/1234.xml I get the xml output. When I try to access items/1234.custom I get an error ActionView::MissingTemplate . I can fix it by adding the file app/views/show.custom.ruby with the contents:

@item.to_custom

Is there a way to get to_custom to work like to_xml or to_json in a respond_to/with setup? To just use the to_custom method without needing a template? Or will I have to use a view template that calls the method explicitly?

Answer 1

You'll need to manually add a Renderer for your custom format if you want it to render without explicitly adding a view template.

The Rails built-in formats xml and json have renderers automatically added from within the Rails framework, which is why they work right out of the box and your custom format does not ( source code ).

Try adding this in an initializer or right below where you register your MIME type

# config/initializers/renderers.rb
ActionController::Renderers.add :foo do |object, options|
  self.content_type ||= Mime::FOO
  object.respond_to?(:to_foo) ? object.to_foo : object
end

NOTE: Don't use custom as your format name because it will conflict with a method in the respond_with internals.

There is an excellent blog post that explains building custom Renderers in depth here: http://beerlington.com/blog/2011/07/25/building-a-csv-renderer-in-rails-3/