def touch_atomic_updates(field = nil)
      updates = atomic_updates
      return {} unless atomic_updates.key?("$set")
      touches = {}
      updates["$set"].each_pair do |key, value|
        key_regex = /updated_at|u_at#{"|" + field if field.present?}/
        touches.merge!({ key => value }) if key =~ key_regex
      end
      { "$set" => touches }
    end
def touch_atomic_updates(field = nil)
      updates = atomic_updates
      return {} unless atomic_updates.key?("$set")
      touches = {}
      updates["$set"].each_pair do |key, value|
        key_regex = /updated_at|u_at#{"|" + field if field.present?}/
        touches.merge!({ key => value }) if key =~ key_regex
      end
      { "$set" => touches }
    end
Get the atomic updates for a touch operation. Should only include the
 updated_at field and the optional extra field.

 @api private

 @example Get the touch atomic updates.
   document.touch_atomic_updates

 @param [ Symbol ] field The optional field.

 @return [ Hash ] The atomic updates.

 @since 3.0.6