ActiveFedore attribute w/multiple: false setting to ActiveTriples::Resource

at_resource.rb

require "rdf-vocab"

module Ddr
  module Metadata
    class Identifier < ActiveTriples::Resource

      PREMIS = Ddr::Vocab::PREMIS

      ARK_RE = /^ark:/
      DOI_RE = /^doi:/

      ARK = Ddr::Vocab::Preservation.ark
      DOI = RDF::Vocab::Identifiers.doi

      configure type: PREMIS.Identifier
      property :value, predicate: PREMIS.hasIdentifierValue
      property :type, predicate: PREMIS.hasIdentifierType

      def to_s
	      value.first
      end

      def set_type
	      if value =~ ARK_RE
          self.type = ARK
	      elsif value =~ DOI_RE
          self.type = DOI
	      end
      end

    end
  end
end

datastream.rb

module Ddr
  module Datastreams
    class PreservationMetadataDatastream < ActiveFedora::NtriplesRDFDatastream

      property :permanent_id, predicate: Ddr::Vocab::Preservation.hasPermanentId,
                              class_name: "Ddr::Metadata::Identifier"

      property :permanent_url, predicate: Ddr::Vocab::Preservation.hasPermanentUrl

    end
  end
end

model.rb

module Ddr
  module Models
    module HasPreservationMetadata
      extend ActiveSupport::Concern

      included do
        has_metadata "preservationMetadata",
                     type: Ddr::Datastreams::PreservationMetadataDatastream,
                     versionable: true,
                     control_group: "M"

	      has_attributes :permanent_id, :permanent_url,
                        datastream: "preservationMetadata", multiple: false

        after_create :assign_permanent_id!
      end

      def permanent_id_manager
        @permanent_id_manager ||= Ddr::Managers::PermanentIdManager.new(self)
      end

      def assign_permanent_id!
        permanent_id_manager.assign_later
      end

    end
  end
end