DataMapper: Parent / Child Relationship

I couldn't find an example at datamapper.org /docs for a parent child relationship.
After a little searching, I found the answer in the integration tests.  Here is the example:

 class Node
   include DataMapper::Resource

   def self.default_repository_name
     ADAPTER
   end

   property :id, Integer, :serial => true
   property :name, String

     has n, :children, :class_name => 'Node', :child_key => [ :parent_id ]
   belongs_to :parent, :class_name => 'Node', :child_key => [ :parent_id ]
 end

Hope that helps someone else.