How to do a multipart updatable date with Reform

example.rb

require 'date'

class Applicant
  attr_accessor :date
end

applicant = Applicant.new
applicant.date = Date.new(2014, 10, 13)

require 'reform'

class Form < Reform::Form

  property :date, virtual: true do
    property :day
    property :month
    property :year
  end

  validate :validate_date

  def sync
    result = super
    model.date = parse_date
    result
  end

  def validate_date
    unless valid_date?
      errors.add(:date, "Invalid date")
    end
  end

  def valid_date?
    begin
      parse_date
      true
    rescue ArgumentError => e
      false
    end
  end

  def parse_date
    Date.new(date.year.to_i, date.month.to_i, date.day.to_i)
  end

end

form = Form.new(applicant)

puts "Initial day #{form.date.day}"

form_data = {'date' => {'day' => '1','month' => '12','year' => '2015'}}
#form_data = {'date' => {'day' => '50','month' => '12','year' => '2015'}}

if form.validate(form_data)
  puts "validation passed"
  form.sync
else
  puts "validation failed"
end

puts "Final day in form #{form.date.day}"
puts "Final day in model #{applicant.date.day}"