MADS linkage

Gemfile

source 'https://rubygems.org'

gem 'active-fedora', github: 'projecthydra/active_fedora', branch: 'master'
gem 'linkeddata'

mads.rb

#!/usr/bin/env ruby

# mads demo using AF 7.0 rc3

require 'active-fedora'
require 'linkeddata'

# vocabulary
class MADS < RDF::Vocabulary("http://www.loc.gov/mads/rdf/v1#")
  # MADS classes
  property :ComplexSubject
  property :Topic
  property :MADSScheme

  # MADS properties
  property :isMemberOfMADSScheme

  # elementList and elementList values
  property :componentList
  property :elementList
  property :elementValue
  property :TopicElement
end

# scheme
class MadsScheme < ActiveFedora::Rdf::Resource
  configure type: MADS.MADSScheme
  configure base_uri: "http://library.ucsd.edu/ark:/20775/"
  property :name, predicate: RDF::RDFS.label
end

# topic
class MadsTopic < ActiveFedora::Rdf::Resource
  configure type: MADS.Topic
  property :name, predicate: MADS.authoritativeLabel
  property :scheme, predicate: MADS.isMemberOfMADSScheme, class_name: "MadsScheme"
  property :elementList, predicate: MADS.elementList, class_name: "MadsElementList"
  accepts_nested_attributes_for :scheme, :elementList
end
class MadsElementList < ActiveFedora::Rdf::List
  configure type: MADS.elementList
  property :topicElement, predicate: MADS.TopicElement, class_name: "MadsTopicElement"
  accepts_nested_attributes_for :topicElement
end
class MadsTopicElement < ActiveFedora::Rdf::Resource
  property :elementValue, predicate: MADS.elementValue
  configure :type => MADS.TopicElement
end

# complex subject
class MadsComplexSubjectDatastream < ActiveFedora::RdfxmlRDFDatastream
  resource_class.configure type: MADS.ComplexSubject
  resource_class.configure base_uri: "http://library.ucsd.edu/ark:/20775/"
  property :name, predicate: MADS.authoritativeLabel
  property :scheme, predicate: MADS.isMemberOfMADSScheme
  property :componentList, predicate: MADS.componentList, class_name: "MadsComponentList"
  accepts_nested_attributes_for :componentList, :topic, :scheme
  delegate :topic_attributes=, to: :componentList
  alias_method :topic, :componentList
end
class MadsComplexSubject < ActiveFedora::Base
  has_metadata :name => "damsMetadata", :type => MadsComplexSubjectDatastream
  has_attributes :name, :componentList, :scheme, datastream: "damsMetadata", multiple: false
  delegate :componentList_attributes=, to: :damsMetadata
  delegate :topic_attributes=, to: :damsMetadata
  delegate :scheme_attributes=, to: :damsMetadata
end
class MadsComponentList < ActiveFedora::Rdf::List
  configure type: MADS.componentList
  property :topic, predicate: MADS.Topic, class_name: "MadsTopic"
  accepts_nested_attributes_for :topic
end

# complex subject
complex_subject_params = {
  name: 'Civilization, Modern',
  scheme_attributes: [{
    id: 'http://library.ucsd.edu/ark:/20775/bb3333333x',
    name: 'Library of Congress Subject Headings'
  }],
  componentList_attributes: [{
    topic_attributes: [{
        id: 'http://library.ucsd.edu/ark:20775/bb2222222x',
        name: 'Civilization, Modern',
        elementList_attributes: [{
          topicElement_attributes: [{elementValue:"Civilization, Modern"}]
        }],
        scheme_attributes: [{
          id: 'http://library.ucsd.edu/ark:20775/bb4444444x',
          name: 'Library of Congress Subject Headings'
        }]
      }
    ]
  }]
}
sub = MadsComplexSubject.new(pid:'bb1111111x')
sub.attributes = complex_subject_params
puts sub.damsMetadata.content

output.rdf.xml

<?xml version='1.0' encoding='utf-8' ?>
<rdf:RDF xmlns:ns0='http://www.loc.gov/mads/rdf/v1#'
         xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'
         xmlns:rdfs='http://www.w3.org/2000/01/rdf-schema#'>
  <ns0:MADSScheme rdf:about='http://library.ucsd.edu/ark:20775/bb4444444x'>
    <rdfs:label>Library of Congress Subject Headings</rdfs:label>
  </ns0:MADSScheme>
  <ns0:ComplexSubject rdf:about='http://library.ucsd.edu/ark:/20775/bb1111111x'>
    <ns0:authoritativeLabel>Civilization, Modern</ns0:authoritativeLabel>
    <ns0:componentList rdf:parseType='Collection'>
      <ns0:Topic rdf:nodeID='g70290732937020'>
        <ns0:authoritativeLabel>Civilization, Modern</ns0:authoritativeLabel>
        <ns0:elementList rdf:parseType='Collection'>
          <ns0:TopicElement rdf:nodeID='g70290732966240'>
            <ns0:elementValue>Civilization, Modern</ns0:elementValue>
          </ns0:TopicElement>
        </ns0:elementList>
        <ns0:isMemberOfMADSScheme rdf:resource='http://library.ucsd.edu/ark:20775/bb4444444x' />
      </ns0:Topic>
    </ns0:componentList>
    <ns0:isMemberOfMADSScheme rdf:resource='http://library.ucsd.edu/ark:/20775/bb3333333x' />
  </ns0:ComplexSubject>
</rdf:RDF>

I see two issues in the RDF output above:

1. The topic_attributes hash includes an id property, but the generated Topic element has an auto-generated rdf:nodeID instead of using the id for rdf:about. By contrast, the MADSScheme objects are clearly getting assigned RDF subject by the id properties in their hashes.
2. The MADSScheme linked to from Topic (bb4444444x) shows up, but the one linked to from ComplexSubject (bb3333333x) is missing.

Answers are here (edit: I had the numbering reversed, previously.):

1. This was a bug that caused nodes created directly with #attributes= (bypassing Rdf::Term#build) to skip setting their subjects. I have a pull request in for this. It should be fixed in 7.0.2 and later.
2. You need to set the class_name on L55. property :scheme, predicate: MADS.isMemberOfMADSScheme, class_name: "MadsScheme". Without this, the node gets built as a generic Rdf::Resource, and when #attributes= tries to set :name, it fails (unfortunately, silently) since Rdf::Resource has no such property. We should consider a better failure state for this. Obviously, something should happen when you try to pass attributes that don't exist. On the other hand, I'm not sure how hard of a failure is desirable.

There's now a PR in for error messages in #attributes=. With that, your gist should fail at L97 with ArgumentError: No association found for name name'. Has it been defined yet?`.

Hopefully this resolves both issues.