# File lib/dm-core/associations/relationship.rb, line 47
      def parent_key
        @parent_key ||= begin
          parent_key = nil
          parent_model.repository.scope do |r|
            parent_key = if @parent_properties
              parent_model.properties(r.name).slice(*@parent_properties)
            else
              parent_model.key
            end
          end
          PropertySet.new(parent_key)
        end
      end