Deferred ActiveRecord touches

deferred_touch.rb

# When using this, be careful about your testing transactions.
# ActiveRecord after_commit hooks don't play nice with transactional fixtures
# consider adding the test_after_commit gem to your test group
ActiveRecord::Base.class_eval do
  DEFERRED_KEY = "deferred"

  def touch_with_defer(name = nil)
    raise ActiveRecordError, "cannot touch on a new record object" unless persisted?
    defer_until_commit([self.class.name, id, name, "touch"].map(&:to_s).join(":")) { touch_without_defer(name) }
  end
  alias_method_chain :touch, :defer

  private

  def defer_until_commit(key, &block)
    logger.debug "block deferred until commit with key #{key}"
    if set = Thread.current[DEFERRED_KEY] ||= {}
      logger.debug "skipping a duplicate deferral of key #{key}" if set[key].present?
      set[key] ||= block
    end
  end

  after_commit do
    logger.debug "Flushing deferred queue"
    while (set = Thread.current[DEFERRED_KEY]).present?
      # Remove keys from the hash to be safely re-entrant
      set.keys.each do |k|
        logger.debug "undefer block with key #{k}"
        set.delete(k).call
      end
    end
  end

  after_rollback do
    Thread.current[DEFERRED_KEY] = nil
  end
end