Value object that replaced an enum

organisation.rb

# app/models/organisation.rb

# schema like:
#
#  create_table "organisations", id: :uuid, default: -> { "public.gen_random_uuid()" }, force: :cascade do |t|
#    t.string "transponder", default: "my_laps", null: false
#    

class Organisation < ApplicationRecord
  attribute :transponder, TransponderType.new

transponder.rb

# app/lib/transponder.rb

module Transponder
  class << self
    def find(transponder_name)
      transponders[transponder_name.to_sym] || Transponder::None
    end

    def register_transponder(transponder_name, klass)
      transponders[transponder_name.to_sym] = klass
    end

    def known
      transponders.keys
    end

    private
      def transponders
        @_transponders ||= {}
      end
  end

  class Base
    include Comparable

    def self.identifier
      name.demodulize.underscore.to_sym
    end

    def inspect
      "#<Transponder:#{self.class.identifier}>"
    end

    def description
      raise NotImplementedError
    end

    def format_description
      raise NotImplementedError
    end

    def input_pattern
      raise NotImplementedError
    end

    def regex
      raise NotImplementedError
    end

    def normalize(value)
      return nil if value.blank?
      value.strip.upcase
    end

    def valid?(value)
      regex.match?(value)
    end

    def <=>(other)
      self.class <=> other.class
    end

    def to_s
      self.class.identifier.to_s
    end

    def to_partial_path
      "transponders/#{self}"
    end

    def blank?
      false
    end

    private
      def self.inherited(subclass)
        Transponder.register_transponder(subclass.identifier, subclass)
      end
  end

  class None < Base
    def description
      "None"
    end

    def regex
      //
    end

    def format_description
      "(blank)"
    end

    def blank?
      true
    end

    def to_s
      ""
    end

    def input_pattern
      ""
    end

    def to_partial_path
      "transponders/none"
    end
  end

  class MyLaps < Base
    def description
      "MyLaps"
    end

    def format_description
      "AA-12345"
    end

    def input_pattern
      '^[a-zA-Z]{2}-\d{5}$'
    end

    def regex
      /\A[a-zA-Z]{2}-[0-9]{3,8}\z/
    end
  end

  class HexQuad < Base
    def description
      "Hex Quad"
    end

    def format_description
      "four hex digits"
    end

    def input_pattern
      '^[0-9A-Fa-f]{4}$'
    end

    def regex
      /\A[0-9A-F]{4}\z/
    end
  end
end

transponder_type.rb

# app/types/transponder_type.rb

class TransponderType < ActiveModel::Type::Value
  def cast(value)
    case value
    when String, Symbol then Transponder.find(value).new
    when Transponder::Base then value
    when nil then Transponder::None
    else fail TypeError, "can't make Transponder from #{value.inspect}"
    end
  end

  def serialize(value)
    value.to_s
  end
end