Copying validation errors from one attribute to another

When using virtual attributes, the attached trait Show archive.org snapshot can be useful to automatically copy errors from one attribute to another.

Here is a typical use case where Paperclip creates a virtual attribute :attachment, but there are validations on both :attachment and :attachment_file_name. If the form has a file picker on :attachment, you would like to highlight it with errors from any attribute:

Copyclass Note < ActiveRecord::Base
  has_attached_file :attachment
  validates_attachment_presence :attachment
  validates_format_of :attachment_file_name, :with => /^\d+\.jpg$/
  include DoesCopyErrors[from: :attachment_file_name, to: :attachment]
end

If you'd like to remove the errors from the source attribute once they are copied to the target attribute, you can use the :move option:

Copyinclude DoesCopyErors[from: :attachment_file_name, to: :attachment, move: true]