paper_trailでCarrierWaveのフィールドのファイル名のみを保存する

gistfile1.rb

module PaperTrail
  module Model
    module InstanceMethods
      private
        def item_before_change
          attributes.tap do |prev|
            enums = self.respond_to?(:defined_enums) ? self.defined_enums : {}
            changed_attributes.select { |k,v| self.class.column_names.include?(k) }.each do |attr, before|
              before = enums[attr][before] if enums[attr]
              if defined?(CarrierWave::Uploader::Base) && before.is_a?(CarrierWave::Uploader::Base)
                prev[attr] = (before.url && File.basename(before.url))
              else
                prev[attr] = before
              end
            end
          end
        end
    end
  end
end