Gemfile

source 'https://rubygems.org'

gem 'rails', '3.2.13'
gem "active-fedora", :git => "git://github.com/projecthydra/active_fedora.git", :branch => "rdf_nested_attributes"

nested_element_list.rb

#!/usr/bin/env ruby

require "active-fedora"

class MADS < RDF::Vocabulary("http://www.loc.gov/mads/rdf/v1#")
  property :MADSScheme
  property :isMemberOfMADSScheme
  property :authoritativeLabel
  property :elementList
  property :elementValue
  property :Topic
  property :TopicElement
  property :hasExactExternalAuthority
end

class TopicElement
  include ActiveFedora::RdfObject
  rdf_type MADS.TopicElement
  map_predicates do |map|
    map.elementValue(:in=> MADS)
  end
end
class ElementList
  include ActiveFedora::RdfList
end
class Topic
  include ActiveFedora::RdfObject
  rdf_type MADS.Topic
  rdf_subject { |ds| RDF::URI.new(Rails.configuration.id_namespace + ds.pid)}
  map_predicates do |map|
    map.name(:in => MADS, :to => 'authoritativeLabel')
    map.elementList(:in => MADS, :class_name=>'ElementList')
    map.externalAuthority(:in => MADS, :to => 'hasExactExternalAuthority')
  end
  accepts_nested_attributes_for :elementList
end

params = {
  topic: {
    name: "Baseball",
    externalAuthority: "http://id.loc.gov/authorities/subjects/sh85012026",
    elementList: [
      topicElement_attributes: { elementValue: "Baseball" }
    ]
  }
}

topic = Topic.new(RDF::Graph.new)
topic.attributes = params[:topic]
puts topic.graph.dump(:ntriples)

nested_element_list2.rb

#!/usr/bin/env ruby

require "active-fedora"

class MADS < RDF::Vocabulary("http://www.loc.gov/mads/rdf/v1#")
  property :MADSScheme
  property :isMemberOfMADSScheme
  property :authoritativeLabel
  property :elementList
  property :elementValue
  property :Topic
  property :TopicElement
  property :hasExactExternalAuthority
end

class TopicElement
  include ActiveFedora::RdfObject
  rdf_type MADS.TopicElement
  map_predicates do |map|
    map.elementValue(:in=> MADS)
  end
end
class ElementList
  include ActiveFedora::RdfList
end
class Topic
  include ActiveFedora::RdfObject
  rdf_type MADS.Topic
  rdf_subject { |ds| RDF::URI.new(Rails.configuration.id_namespace + ds.pid)}
  map_predicates do |map|
    map.name(:in => MADS, :to => 'authoritativeLabel')
    map.elementList(:in => MADS, :class_name=>'ElementList')
    map.externalAuthority(:in => MADS, :to => 'hasExactExternalAuthority')
  end
  accepts_nested_attributes_for :elementList
end

params = {
  topic: {
    name: "Baseball",
    externalAuthority: "http://id.loc.gov/authorities/subjects/sh85012026",
  },
  topicElement: {
    elementValue: "Baseball"
  }
}

topic = Topic.new(RDF::Graph.new)
topic.attributes = params[:topic]

topicElement = TopicElement.new(RDF::Graph.new)
topic.attributes = params[:topicElement]

elementList = ElementList.new(RDF::Graph.new,RDF::Node.new)
elementList[0] = topicElement
topic.elementList = elementList

puts topic.graph.dump(:ntriples)

output

output from "bundle exec ./nested_element_list.rb":

_:bn1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.loc.gov/mads/rdf/v1#Topic> .
_:bn1 <http://www.loc.gov/mads/rdf/v1#authoritativeLabel> "Baseball" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#hasExactExternalAuthority> "http://id.loc.gov/authorities/subjects/sh85012026" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#elementList> "{:topicElement_attributes=>{:elementValue=>\"Baseball\"}}" .

output from "bundle exec ./nested_element_list2.rb":

_:bn1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.loc.gov/mads/rdf/v1#Topic> .
_:bn1 <http://www.loc.gov/mads/rdf/v1#authoritativeLabel> "Baseball" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#hasExactExternalAuthority> "http://id.loc.gov/authorities/subjects/sh85012026" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#elementList> "#<ElementList:0x007f84d229db88>" .

expected:

_:bn1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.loc.gov/mads/rdf/v1#Topic> .
_:bn1 <http://www.loc.gov/mads/rdf/v1#authoritativeLabel> "Baseball" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#hasExactExternalAuthority> "http://id.loc.gov/authorities/subjects/sh85012026" .
_:bn1 <http://www.loc.gov/mads/rdf/v1#elementList> _:bn2 .
_:bn2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#first> _:bn3 .
_:bn2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#rest> <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> .
_:bn3 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.loc.gov/mads/rdf/v1#TopicElement> .
_:bn3 <http://www.loc.gov/mads/rdf/v1#elementValue> "Baseball" .