child_key (DataMapper::Associations::ManyToOne::Relationship)

    # File lib/dm-core/associations/many_to_one.rb, line 39
            def child_key
              return @child_key if defined?(@child_key)

              repository_name = child_repository_name || parent_repository_name
              properties      = child_model.properties(repository_name)

              child_key = parent_key.zip(@child_properties || []).map do |parent_property, property_name|
                property_name ||= "#{name}_#{parent_property.name}".to_sym

                properties[property_name] || begin
                  # create the property within the correct repository
                  DataMapper.repository(repository_name) do
                    type = parent_property.send(parent_property.type == DataMapper::Types::Boolean ? :type : :primitive)
                    child_model.property(property_name, type, child_key_options(parent_property))
                  end
                end
              end

              @child_key = properties.class.new(child_key).freeze
            end