# File lib/autumn/datamapper_hacks.rb, line 266
  def parent_key(repository_name=nil)
    repository_name ||= repository.name
    @parent_key ||= Hash.new
    @parent_key[repository_name] ||= begin
      parent_key = nil
      repository(repository_name).scope do |r|
        parent_key = if @parent_properties
          parent_model.properties(repository_name).slice(*@parent_properties)
        else
          parent_model.key(repository_name)
        end
      end
      DataMapper::PropertySet.new(parent_key)
    end
    return @parent_key[repository_name]
  end