Hyundai.rb

# This is a ActiveRecord STI class
class Hyundai < Car
  has_one :hyundai_details
  delegate *HyundaiDetails::ACCESSIBLE_ACCESSOR_METHODS, to: :hyundai_details

  default_scope { includes(:hyundai_details) }
  
  def initialize(args = {})
    hyundai_details_attrs = {}
    args.each do |key, _val|
      if HyundaiDetails::ACCESSIBLE_ATTRS.include?(key)
        hyundai_details_attrs[key] = args.delete(key)
      end
    end

    super(args).tap do
      build_hyundai_details(hyundai_details_attrs) if new_record?
    end
  end
end

HyundaiDetails.rb

class HyundaiDetails < ApplicationRecord
  ACCESSIBLE_ATTRS = %i[graphics color raditude doors wheels].freeze
  ACCESSIBLE_ACCESSOR_METHODS = ACCESSIBLE_ATTRS.map { |attr| [attr, :"#{attr}="] }.flatten.freeze
  
  belongs_to :hyundai
end