Failed attempt to implement generic 'deep copy' for AR... I'm just keeping it to document the thought process and the dead end I've reached.

copyable_attributes.rb

module CopyableAttributes
  def self.included(base)
    def copyable_attributes_keys2
      attributes.keys - self.class.protected_attributes.to_a - [ "created_at", "updated_at"] - foreign_key_list
      # TODO: we also need to remove foreign keys... maybe have class method 'uncopyable_attributes_keys'?
    end

    private

    def relevant_base_class
      baseclass = self.class
      while baseclass.superclass != ActiveRecord::Base
        baseclass = baseclass.superclass
      end
      baseclass
    end
    def foreign_key_list
      baseclass = relevant_base_class
      baseclass.foreign_key_list_recursive
    end
    def foreign_key_list_recursive
      result = self.class.reflections.
        select {|name, refl| refl.macro == :belongs_to }.
        collect {|name, assoc| assoc.foreign_key }
      result << self.class.descendants.collect {|d| d.copyable_attributes_keys2 }
      # TODO: doesn't work, as 'copyable_attributes_keys2' is *not* a static method...
      # we need ClassMethods to do this.
      # TODO: There is an issue with sub classes being loaded only once required,
      # class.descendants might therefore be incomplete (as least in dev mode):
      # see http://stackoverflow.com/questions/5888313/ror-mymodel-descendants-returns-in-a-view-after-the-first-call
    end
  end
end

ActiveRecord::Base.send :include, CopyableAttributes