こういうhas_oneの使い方ってありなんだろうか?

gistfile1.rb

class Entry < ActiveRecord:Base
  has_many :messages
  has_one  :latest_message, -> { merge(Message.latest) }, class_name: 'Message'
end

class Message < ActiveRecord:Base
  scope :latest, -> { order(id: :desc) }
end

gistfile2.txt

irb(main):003:0> @entry = entry.first
  Entry Load (0.2ms)  SELECT  "entries".* FROM "entries"  ORDER BY "entries"."id" ASC LIMIT 1
irb(main):003:0> @entry.latest_message
  Message Load (0.2ms)  SELECT  "messages".* FROM "messages" WHERE "messages"."entry_id" = ?  ORDER BY "messages"."id" DESC LIMIT 1  [["entry_id", 1]]
=> #<Message id: 10, body: "Message9", entry_id: 1, created_at: "2015-06-30 16:06:47", updated_at: "2015-06-30 16:06:47">

よいらしい
編集しないからreadonlyしたほうがいいとのこと