extract-value-object.md

Extract Value Object

http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/

class Rating
  include Comparable

  def self.from_cost(cost)
    if cost <= 2
      new("A")
    elsif cost <= 4
      new("B")
    elsif cost <= 8
      new("C")
    elsif cost <= 16
      new("D")
    else
      new("F")
    end
  end

  def initialize(letter)
    @letter = letter
  end

  def better_than?(other)
    self > other
  end

  def <=>(other)
    other.to_s <=> to_s
  end

  def hash
    @letter.hash
  end

  def eql?(other)
    to_s == other.to_s
  end

  def to_s
    @letter.to_s
  end
end

class ConstantSnapshot < ActiveRecord::Base
  # …

  def rating
    @rating ||= Rating.from_cost(cost)
  end
end