Topic: Aggregation Troubles

I am trying to use composed_of to merge first name and last name from my users table.

users.rb

class User < ActiveRecord::Base
    composed_of :name,
                            :mapping =>[ [:first_name,:first],[:last_name,:last] ]
end

name.rb ( does it belong in the lib directory? )
class Name
attr_reader :first, :last
    def initialize(first, last)
        @first_name = first
        @last_name = last
    end
    def to_s
        [ @first, @last ].compact.join(" ")
    end
end

I have not been able to get Aggregation to work so far.

Any suggestions?