lib/ancestry/class_methods.rb
def build_ancestry_from_parent_ids! parent_id = nil, ancestry = nil
      unscoped_where do |scope|
        scope.where(:parent_id => parent_id).find_each 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
    end
def build_ancestry_from_parent_ids! parent_id = nil, ancestry = nil
      unscoped_where do |scope|
        scope.where(:parent_id => parent_id).find_each 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
    end
Build ancestry from parent id's for migration purposes