delegate

delgate_default.rb

module DelegateDefault
  def self.included base
    base.send :extend, ClassMethods
  end

  module ClassMethods
    def delegate_default args_hsh
      include InstanceMethods
      args_hsh.each do |attr,parent|
        define_method attr do
          default attr, parent
        end
      end
    end
  end

  module InstanceMethods
    def default attr, parent
      result = read_attribute attr
      if result.blank?
        source = send(parent)
        result = source.send(attr) unless source.nil?
      end
      result
    end

  end

end

my_model.rb

class MyModel < ActiveRecord::Base
  belongs_to :item
  delegate_default :price => :item
end