gistfile1.rb

class Subject < ActiveRecord::Base
  validates_presence_of :name
  validates_uniqueness_of :name
  acts_as_tree

  class << self
    @@all_subjects =[]

    def get_all_childrens_recursive parent
      return if parent == nil
      return if parent.children == nil
      return if parent.children.empty?
      childrens = parent.children
      childrens.each do |children|
        @@all_subjects  <<= children
        get_all_childrens_recursive children
      end   
    end
    
    def get_all_childrens
      root = self.root
      @@all_subjects =  []
      @@all_subjects  <<= root
      get_all_childrens_recursive root
      @@all_subjects  
    end

  end
end