Rebuild method can't work with namespaced controllers and models

If I have namespaced controller and model

module Stock
  class CategoriesController < ApplicationController
    include ::TheSortableTreeController::Rebuild

class Stock::Category < ActiveRecord::Base
  acts_as_nested_set 
  include ::TheSortableTree::Scopes

This method form gem won't work

module DefineVariablesMethod
    public
    def the_define_common_variables
      collection = self.class.to_s.split(':').last.sub(/Controller/,'').underscore.downcase                 # 'recipes'
      collection = self.respond_to?(:sortable_collection) ? self.sortable_collection : collection           # 'recipes'
      variable   = collection.singularize                                                                   # 'recipe'
      klass      = self.respond_to?(:sortable_model) ? self.sortable_model : variable.classify.constantize  #  Recipe
      ["@#{variable}", collection, klass]
    end
  end

Because this line

collection = self.class.to_s.split(':').last.sub(/Controller/,'').underscore.downcase

Will result "categories"

And here klass = self.respond_to?(:sortable_model) ? self.sortable_model : variable.classify.constantize

you will get error

*** NameError Exception: uninitialized constant Category

Because the class is not Category but Stock::Category

the-teacher / the_sortable_tree

Rebuild method can't work with namespaced controllers and models #91