# File lib/couchrest/model/designs/view.rb, line 242
        def keys(*keys)
          if keys.empty?
            rows.map{|r| r.key}
          else
            raise "View#keys cannot by used when key or startkey/endkey have been set" unless query[:key].nil? && query[:startkey].nil? && query[:endkey].nil?
            update_query(:keys => keys.first)
          end
        end