Extending ActiveStorage::Attachment - Adding custom fields

Question

I want to extend the class ActiveStorage::Attachment and add an enum attribute for visibility of attachments.

My initial approach was to create a new file attachment.rb in the \app\models directory as follows.

class ActiveStorage::Attachment < ActiveRecord::Base
    enum visibility: [ :privately_visible, :publicly_visible]
end

This doesn't work.

Any suggestions are welcome. What's the Rails way to extend classes?

Update

I have a solution that works partially now. For this, I have created an extension active_storage_attachment_extension.rb and placed it in \lib

module ActiveStorageAttachmentExtension

  extend ActiveSupport::Concern

  included do
    enum visibility: [ :privately_visible, :publicly_visible]

    def describe_me
      puts "I am part of the extension"
    end

  end
end

The extension is loaded during initialization in extensions.rb

ActiveStorage::Attachment.send(:include, ::ActiveStorageAttachmentExtension)

Unfortunately, it is only working partly: While the enum methods publicly_visible? and privately_visible? are available in the views, they are not available in the controller. When invoking any of the methods in the controller, then the enum seems to have disappeared. I get a "NoMethodError - undefined method" error. Surprisingly, once the enum methods are called once in the controller, they are also not available any more in the views. I assume that the ActiveStorage::Attachment class gets reloaded dynamically and that the extensions are lost as they are only added during initialization.

Any ideas?

Answer 1

This works for me in Rails 6.

# frozen_string_literal: true

module ActiveStorageAttachmentExtension
  extend ActiveSupport::Concern

  included do
    has_many :virus_scan_results
  end
end

Rails.configuration.to_prepare do
  ActiveStorage::Attachment.include ActiveStorageAttachmentExtension
end