Register an ActiveModel attribute type with the ability to pass options to it?

Question

Is it possible to use ActiveModel::Type.register in a way that still lets you pass arguments?

To demonstrate, is it possible to turn this:

class Action < ApplicationRecord
  attribute :type, Types::VirtualStringType.new(suffix: 'Action')
end

into something like

class Action < ApplicationRecord
  attribute :type, :virtual_string, suffix: 'Action'
end

Answer 1

You can register a new type by creating config/initializers/active_record_types.rb

Rails.application.config.to_prepare do
  ActiveRecord::Type.register(:virtual_string, Types::VirtualStringType)
end

The type class would have to accept the options/arguments in initialize like this:

def initialize(**args)
  @suffix = args[:suffix].to_s
end

Here's a sample implementation:

module Types
  class VirtualStringType < ActiveRecord::Type::String
    def initialize(**args)
      @suffix = args[:suffix].to_s
    end

    def cast_value(value)
      value.to_s + @suffix unless value.nil?
    end

    def serialize(value)
      value.chomp(@suffix) unless value.nil?
    end

    def changed_in_place?(original_value_for_database, value)
      original_value_for_database != serialize(value)
    end
  end
end