def to_xml
      db = @local_db || @db || return
      Nokogiri::XML::Builder.new(encoding: "UTF-8") do |xml|
        xml.documents do
          xml.parent.add_child db.all.join(" ")
        end
      end.to_xml
    end
def to_xml
      db = @local_db || @db || return
      Nokogiri::XML::Builder.new(encoding: "UTF-8") do |xml|
        xml.documents do
          xml.parent.add_child db.all.join(" ")
        end
      end.to_xml
    end
list all entries as a serialization
 @return [String]