ActiveRecord with value object

AR_VALUE.rb

require "bundler/inline"

gemfile(false) do
  source "https://rubygems.org"
  gem "rspec"
  gem "pry"
  gem "activerecord"
  gem "sqlite3"
end

require 'rspec'
# require 'rspec/autorun'

RSpec.configure do  |c|
  c.filter_run :focus
end

require "active_record"
require "logger"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :planets, force: true do |t|
    t.string  :name
    t.integer :size_amount
    t.string  :size_unit
  end
end

Size = Struct.new(:number, :unit) do
  def to_s
    "#{number} #{unit}"
  end

  alias inspect to_s
end

class Planet < ActiveRecord::Base

  def size=(new_size)
    self.size_amount = new_size.number
    self.size_unit = new_size.unit
    self
  end

  def size
    Size.new(size_amount, size_unit)
  end
end

earth = Planet.create(name: 'Earth', size: Size.new(1, :mile))

puts earth.inspect