Build object attributes using a hash and a related object to build that hash

dog_builder.rb

require 'active_model'
require 'active_support'

class Dog
  include ActiveModel::Model
  attr_accessor :name, :age

  def self.build(attr_hash)
    Dog.new DogBuilder.attributes(attr_hash)
  end

end

class DogBuilder
  def self.attributes(hash)
    {
      name: hash[:name],
      age: calculate_age(hash)
    }
  end

  def self.calculate_age(hash)
    # do a calculation based on hash[:birthday], for example, here
    Time.now.year - hash[:birthyear]
  end
end

puts (Dog.build({name: "Lucy", birthyear: 2010})).inspect