Polymorphic associations: finding object types

Hi there

I'm developing an application which makes use of RoR's polymorphic associations to associate several components with a single product, like so:

class Product < ActiveRecord::Base   has_many :line_items, :before_add => :validate_addition end

class LineItem < ActiveRecord::Base   belongs_to :product   belongs_to :resource, :polymorphic => true end

class Circuit < ActiveRecord::Base   has_one :line_item, :as => :resource end

class UserAccount < ActiveRecord::Base   has_one :line_item, :as => :resource end

I'd like to be able to obtain a list of the objects which act as a resource for use in the interface. I could do this from the database like so: