Migrations that make ActiveStorage attachments work with UUID primary keys. https://github.com/rails/rails/pull/32466

001_add_record_uuid_to_active_storage_attachments.rb

class AddRecordUuidToActiveStorageAttachments < ActiveRecord::Migration[5.2]
  def change
    # After applying this migration, you'll need to manually go through your
    # attachments and populate the new `record_uuid` column.
    # If you're unable to do this, you'll probably have to delete all your attachments.
    # You've pretty much got useless garbage data if that's the case :(
    add_column :active_storage_attachments, :record_uuid, :uuid
  end
end

002_change_active_storage_attachments_record_id_to_uuid.rb

class ChangeActiveStorageAttachmentsRecordIdToUuid < ActiveRecord::Migration[5.2]
  def up
    remove_record_id_index!

    # Rename the built-in record_id:int column and allow NULL values.
    rename_column :active_storage_attachments, :record_id, :record_id_int
    change_column_null :active_storage_attachments, :record_id_int, true

    # Rename our (now populated) UUID column to `record_id` and prevent NULL values.
    rename_column :active_storage_attachments, :record_uuid, :record_id
    change_column_null :active_storage_attachments, :record_id, false

    add_record_id_index!
  end

  def down
    remove_record_id_index!

    # Rename our UUID column back to `record_uuid` and once again allow NULL values.
    rename_column :active_storage_attachments, :record_id, :record_uuid
    change_column_null :active_storage_attachments, :record_uuid, true

    # Rename `record_id_int` back to record_id:int column and prevent NULL values.
    rename_column :active_storage_attachments, :record_id_int, :record_id
    change_column_null :active_storage_attachments, :record_id, false

    add_record_id_index!
  end

  private

  def add_record_id_index!
    add_index :active_storage_attachments, [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
  end

  def remove_record_id_index!
    remove_index :active_storage_attachments, column: [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
  end
end