Is it okay to call a private method of a parent class's subclass from a module which is included in the parent class in rails?

Question

Is it okay to call a private method of a parent class's subclass from a module which is included in the parent class especially when it concerns ApplicationController, Controllers and lib modules in Rails?

Consider if required to change the controller name the method name to reflect the model name(to Article) change.

I feel this is really bad coding and wanted to know what community thinks about this

Example from a Rails Application:

/lib/some_module.rb

module SomeModule
  include SomeModuleResource

  def filtering_method
    calling_method
  end

  def calling_method
    fetch_object
  end
end

/lib/some_module_resource.rb

module SomeModuleResource
  def fetch_object
    note
  end
end

/app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  include SomeModule

  before_action :filtering_method

end

/app/controllers/notes_controller.rb

class NotesController < ApplicationController

  def show
  end

  private

  def note
    @note ||= Note.find(param[:id]))
  end
end

Answer 1

I'm of the opinion that this is not necessary bad, although when you expect a certain interface (methods, variables, etc.) from the class that includes the module I would add the following:

module SomeModuleResource
  def fetch_object
    note
  end

  private

  def note
    raise NotImplementedError
  end
end

This way, when #note is called without implementing it (because you forgot it was needed or whatever) a NotImplementedError is raised.

Another option is to work around it and create a more general solution. For example, if all controllers behave the same way you described above you can do the following:

module SomeModuleResource
  def fetch_object
    note
  end

  private

  def note
    klass = params[:controller].classify.constantize
    instance = klass.find(params[:id])

    var_name = "@#{klass.underscore}"
    instance_variable_set(var_name, instance) unless instance_variable_get(var_name)
  end
end

You could also create a class helper method like before_action so that you can pass your own implementation.

module SomeModule
  include SomeModuleResource

  def self.included(base)
    base.extend(ClassMethods)
  end

  def filtering_method
    calling_method
  end

  def calling_method
    fetch_object
  end

  module ClassMethods
    def custom_before_action(&block)
      define_method(:note, &block)
      private :note

      before_action :filtering_method
    end
  end
end

Now you can use custom_before_filter { @note ||= Note.find(params[:id]) } in every controller (after including).

The above is just to present you with ideas. I'm sure you could find better solution to the problem, but this hopefully points you in the right direction.

See: Alternatives to abstract classes in Ruby?. Or search for abstract classes in Ruby and you'll find more on this subject.