# File lib/active_record/acts/tree.rb, line 35
        def acts_as_tree(options = {})
          configuration = { :foreign_key => "parent_id", :order => nil, :counter_cache => nil }
          configuration.update(options) if options.is_a?(Hash)

          belongs_to :parent, :class_name => name, :foreign_key => configuration[:foreign_key], :counter_cache => configuration[:counter_cache]
          has_many :children, :class_name => name, :foreign_key => configuration[:foreign_key], :order => configuration[:order], :dependent => true

          module_eval "def self.roots\nself.find(:all, :conditions => \"\#{configuration[:foreign_key]} IS NULL\", :order => \"\#{configuration[:order]}\")\nend\ndef self.root\nself.find(:first, :conditions => \"\#{configuration[:foreign_key]} IS NULL\", :order => \"\#{configuration[:order]}\")\nend\n"

          define_method(:siblings) do
            if parent
              self.class.find(:all, :conditions => [ "#{configuration[:foreign_key]} = ?", parent.id ], :order => configuration[:order])
            else
              self.class.roots
            end
          end
        end