touchless_simple.rb

require 'active_support/concern'

module Touchless
  module TouchLater
    extend ActiveSupport::Concern

    included do
      # Preserve immediate touch behavior as touch_now
      alias_method :touch, :touch_now
      alias_method :touch_later, :touch

      # TODO: only want this callback registered if touch was called,
      # so untouched records needn't be tracked by the transaction.
      before_commit :defer_touch_until_commit
    end

    # Defer touch until just before the db transaction commits. Rely on
    # after_touch callbacks to fire and bubble touches (also deferred until
    # transaction commit) up to parents.
    def touch_later(*names)
      raise ActiveRecordError, "cannot touch on a new record object" unless persisted?

      # Mark the usual suspects plus the attrs requested for later touching
      @_touch_attrs ||= timestamp_attributes_for_update_in_model
      @_touch_attrs |= names

      # Update this record's timestamps, but don't mark them as changed so
      # this record doesn't get sucked in to a belongs_to autosave.
      surreptiously_touch attrs
      connection.add_transaction_record self
    end

    # Touch these attributes, but pretend like nothing changed so they don't
    # get swept up and automatically saved when the associated record saves.
    private def surreptiously_touch(attrs)
      @_touch_time = current_time_from_proper_timezone
      attrs.each { |attr| write_attribute attr, @_touch_time }
      clear_attribute_changes attrs.keys
    end

    private def defer_touch_until_commit
      if @_touch_attrs.present?
        # TODO: accept an optional time: argument rather than always using
        # the current time.
        touch_now *@_touch_attrs, time: @_touch_time
      end
    end
  end
end

# Wire up Active Record when it's available.
require 'activesupport/lazy_load_hooks'
ActiveSupport.on_load :active_record do
  include ::Touchless::TouchLater
end