pull_up_errors.rb

module PullUpErrors
  extend ActiveSupport::Concern

  # Used to pull up errors that are on an associated collection or object

  included do
    after_validation :pull_up_errors

    def pull_up_errors(*attrs)
      @pull_up_attrs = Array(attrs)
    end
  end

  # after_validation:
  # We want the individual validation error messages on the specified attrs to be pulled
  # up to this instance's errors collection.
  def pull_up_errors
    @@pull_up_attrs.each do |attr|
      association = self.__send__(attr)
      next unless association

      Array(association).each do |instance|
        if instance.errors.present?
          instance.errors.full_messages.each { |msg| errors.add(attr, msg) }
        end
      end
      errors[attr].delete("is invalid")
    end
  end
end