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DDEX metadata serialization for Ruby


require "ddex"

message ="path/to/metadata.xml")  # ERN
puts message.update_indicator
message.resource_list.sound_recordings.each do |sr|
  title = sr.reference_title.title_text
  puts title.value
  puts title.language_and_script_code
  puts sr.remastered?

puts "Supported!" if DDEX.supports?("ern/341")

message =
message =
p message.to_hash

include DDEX::ERN::V341   # v3.4.1
message = =>
record  = => "en-US")
# ...
message.resource_list.sound_recordings = [record]

xml = DDEX.write(message)"bloat.xml", "w") { |io| io.puts(xml) }



gem install ddex


gem "ddex"

Supported Versions


How This Differs From the Spec

Every DDEX version handled by this module is fully supported, but there are some things you'll need to know.

Naming Conventions

DDEX elements and attributes use the CamelCase naming convention, this module uses Ruby naming conversions: CamelCase for classes, and snake_case for class attributes. For example, this DDEX XML:


Would be manipulated via:

party = => "sshaw")
puts party.full_name
party.full_name = "gwozdzie"

See also Boolean elements and attributes


Elements that can occur more than once will be placed in an Array and their parent classes' accessor methods will use the plural form of the element/attribute's name. For example:

  <!-- More data -->
    <PLineText>Track Copyright</PLineText>
    <PLineText>Another Track Copyright</PLineText>

Would be manipulated via:

release.p_lines.each { |line| puts line.p_line_text }
release.p_lines << => 1999)

Boolean Elements and Attributes

The following are applied to accessors derived from DDEX elements and attributes with an XML schema type of boolean:

  • "Is" is removed from the beginning of the name

  • The reader method is turned into a predicate accessor, i.e., has a "?" appended to it

For example, SoundRecording/IsArtistRelated:

recording = => true)
p recording.artist_related?  # true
recording.artist_related = false

Version Specific Changes

These changes only affect the object model, the resulting XML will conform to the appropriate DDEX schema.

ERN >= v3.6

PriceInformation/@PriceType has been renamed to PriceInformation#type to avoid conflicting with the element of the same name (PriceInformation/PriceType).

Specification Version Detection

The specification version is determined by the MessageSchemaVersionId, which can be:

  1. Detected based on the root element's value i.e., /node()/@MessageSchemaVersionId (the root element varies by specification)

  2. Explicitly given to via the :version option

By default the MessageSchemaVersionId is assumed to be in SPEC/VERSION or VERSION format (any leading, trailing, or duplicate slashes will be stripped), as this seems to be the convention used by most instance docs -though the DDEX specifications are not strict about this. If you're dealing with MessageSchemaVersionIds that vary from this format, and explicitly setting the version is not practical, you can set the global default(s):

DDEX::ERN.config["V35"][:message_schema_version_id] = "ern tray_fever!"
DDEX::ERN.config["V351"][:message_schema_version_id] = "ern/35-punto-1"
# ...

Note that the version key must match the version's module name.

Feel free to open an issue if you feel this arrangement is problematic or should be modified to accommodate something else.


Not yet!

DDEX Parsing Service (Rack Endpoint)

If you want to parse DDEX metadata but don't want to use Ruby to process the results you can setup a parsing service using Rack::DDEX. Rack::DDEX is a Rack endpoint that parses a DDEX file and returns JSON.

For example, from the repository's root:

~/code/ruby/ddex >cat etc/
require "rack/ddex"


~/code/ruby/ddex >rackup -I lib etc/  # Note that -D has problems with autoloading
[2014-12-15 20:35:40] INFO  WEBrick 1.3.1
[2014-12-15 20:35:40] INFO  ruby 2.1.2 (2014-05-08) [x86_64-darwin13.0]
[2014-12-15 20:35:40] INFO  WEBrick::HTTPServer#start: pid=76385 port=9292

Then, from another terminal

~/code/ruby/ddex >curl -d @spec/fixtures/ern/36/instance1.xml http://localhost:9292

~/code/ruby/ddex >curl http://localhost:9292  # HTTP 400
{"error":"XML parsing error: Start tag expected, '<' not found"}



More Info

TODO/Known Problems

  • ROXML.from_xml does not check the root element's name. Need to add something like:

    raise "unknown element #{}" unless == tag_name
  • When an ROXML accessor expects an ROXML class, and one is not provided, to_xml will result in a NoMethodError:

    # in SomeClass
    xml_accessor :x, :as => AnotherClass
    # Then
    x = => "123")
    x.to_xml  # undefined method `to_xml' for "123":String

    Raised here:

See Also


Skye Shaw [ {AT}]


Copyright © 2013 Skye Shaw. Released under the MIT License.

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