# File lib/ancestry/class_methods.rb, line 145
    def build_ancestry_from_parent_ids! parent_id = nil, ancestry = nil
      self.base_class.find_each(:conditions => {:parent_id => parent_id}) do |node|
        node.without_ancestry_callbacks do
          node.update_attribute ancestry_column, ancestry
        end
        build_ancestry_from_parent_ids! node.id, if ancestry.nil? then "#{node.id}" else "#{ancestry}/#{node.id}" end
      end
    end