through (DataMapper::Associations::ManyToMany::Relationship)

    # File lib/dm-core/associations/many_to_many.rb, line 52
            def through
              return @through if defined?(@through)

              if options[:through].kind_of?(Associations::Relationship)
                return @through = options[:through]
              end

              repository_name = source_repository_name
              relationships   = source_model.relationships(repository_name)
              name            = through_relationship_name

              @through = relationships[name] ||
                DataMapper.repository(repository_name) do
                  source_model.has(min..max, name, through_model, one_to_many_options)
                end

              @through.child_key

              @through
            end