Disable auto rendering in rails - ruby-on-rails

Question

What I need is to disable the automatic page (HTML) rendering in rails and override it with a after_action method. What I'm trying to achieve is an equivalent of CakePHP $this->autoRender = false;
application_controller.rb
class ApplicationController < ActionController::Base
after_action :custom_render
layout nil # Tried this but didn't worked
def custom_render
render #[...]
end
end
some_controller.rb
class SomeController < ApplicationController
def index
# No rendering here
end
end
As shown in the code I tried to add a layout nil to prevent all actions from rendering, but that doesn't seem to affect the behaviour of the action.

Answer 1

Haven't checked whether it works with Rails 4, but this patch works for Rails 5.
According to the code of BasicImplicitRender and ImplicitRender, send_action of is BasicImplicitRender responsible for calling default_render
Documentation says:
For API controllers, the implicit response is always 204 No Content.
For all other controllers, we use ... heuristics to decide whether to
render a template, raise an error for a missing template, or respond with
204 No Content ...
So I suppose redefining default_render method will serve you purpose.
In your controller:
def a
# uses `default_render` unless you call `render` method explicitly
end
def b
render plain: 'Custom text for b' # `default_render` won't be called
end
private
# This does the trick
#
def default_render
render plain: 'Text'
end
You may also hack send_action just like it is done in Rails so as to even skip default_render call at all:
module ActionController
module BasicImplicitRender # :nodoc:
def send_action(method, *args)
# super.tap { default_render unless performed? }
super
end
end
end

Answer 2

To disable rendering (well return nothing) issue.
def index
render :nothing
end
But it's too late to do anything, as it will return response with empty body.
To disable layout:
def index
render layout: false
end
This will render you view without a layout, issue (render layout: 'my_custom_layout') to render default view but with different layout.
We don't know what you want, but the simplest solution is just to render a specific view, f.i.:
def index
render 'my_custom_file.'
end
There are really many options: http://guides.rubyonrails.org/layouts_and_rendering.html#using-render
EDIT - as requested in a comment
class ApplicationController < ActionController::Base
before_action :set_user_template
# ...
def set_user_template
template_name = current_user.template_name
self.class.layout "#{template_name}/application"
end
end