Where to put Ruby helper methods for Rails controllers?

You can call any helper methods from a controller using the view_context, e.g.

view_context.my_helper_method

You should define the method inside ApplicationController.

you should define methods inside application controller, if you have few methods then you can do as follow

class ApplicationController < ActionController::Base    
  helper_method :first_method
  helper_method :second_method

  def first_method
    ... #your code
  end

  def second_method
    ... #your code
  end
end

You can also include helper files as follow

class YourController < ApplicationController
  include OneHelper
  include TwoHelper
end

For Rails 4 onwards, concerns are the way to go. There was a decent article which can still be viewed via the Wayback Machine.

In essence, if you look in your controllers folder you should see a concerns sub-folder. Create a module in there along these lines

module EventsHelper
  def do_something
  end
end

Then, in the controller just include it

class BadgeController < ApplicationController
  include EventsHelper

  ...
end