RoR: Lock values validation

en.yml

en:
  errors:
      messages:
        lock: can't be changed

lock_validator.rb

# app/validators/lock_validator.rb

class LockValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    lock_values = options[:values] || []
    changed = record.send("#{attribute}_changed?")
    value_was = record.send("#{attribute}_was")
    if changed && lock_values.include?(value_was)
      record.errors.add(attribute.to_sym, :lock)
    end
  end
end

page.rb

class Page < ActiveRecord::Base
  KINDS = {
    home: 'home',
    about_us: 'about-us'
  }.freeze
  
  validates :uid, lock: { values: Sample::KINDS.values }
end