Better way to detect if a story has subtasks?

I am writing some transition changes that will do different things depending on the existence or non-existence of an issue's subtasks. The status of the subtask is unimportant, so the condition that checks subtask status doesn't help.

The best I can come up with is to create a field such as "Subtask Exists" and have the action that creates a subtask write a "1" into the subtask's field, and then copy the contents of that field to the parent.

There is the downside of being unable to blank the parent's field if the subtask is deleted. But such deletions are very rare.

Inelegant, but it works.

Anyone have a better idea?