Rails | Active Storage Attachment + acts_as_list

20200119064500_add_position_column_to_active_storage_attachments.rb

# db/migrate/20200119064500_add_position_column_to_active_storage_attachments.rb

class AddPositionColumnToActiveStorageAttachments < ActiveRecord::Migration[6.0]
  def change
    add_column :active_storage_attachments, :position, :integer, default: 0
  end
end

active_storage_attachment.rb

# config/initializers/active_storage_attachment.rb

module ActiveStorageAttachmentList
  extend ActiveSupport::Concern

  included do
    acts_as_list scope: [:record_id]
  end
end

Rails.configuration.to_prepare do
  ActiveStorage::Attachment.send :include, ActiveStorageAttachmentList
end

usage.rb

User.first.sorted_images.last.update(position: 1)

user.rb

# app/models/user.rb

class User < ApplicationRecord
  # Active Storage overrides to sort by position
  has_many :sorted_images, -> { order(position: :asc) }, class_name: "ActiveStorage::Attachment", as: :record, inverse_of: :record, dependent: false
end

Instead of rewriting that has_many just to set order, you can simply set default_scope and let original has_many_attached in model:

module ActiveStorageAttachmentList
  extend ActiveSupport::Concern

  included do
    acts_as_list scope: %i[record_id record_type name]
    default_scope { order(:position) }
  end
end