ember-data polymorphic and rails model

list.coffee

App.List = DS.Model.extend
  project:  DS.BelongsTo(App.Project)
  user:     DS.BelongsTo(App.User)
  task:     DS.BelongsTo(App.Task)
  proposal: DS.BelongsTo(App.Proposal)

list.rb

class List < ActiveRecord::Base
  attr_accessible :name, :project_id, :user_id, :task_id, proposal_id
  belongs_to :listable, :polymorphic => true
  
  %w(user project user proposal).each do |name|
        
    class_eval %(
      def #{name}_id
        listable_id if listable_type == '#{name.classify}'
      end
  
      def #{name}_id=(_value)
        self.listable_id = _value
        self.listable_type = '#{name.classify}'
      end
    )
    
  end


end

list_serializer.rb

class ListSerializer < ActiveModel::Serializer
  attributes :id, :name, :project_id, :user_id, :task_id, proposal_id
end