Updating date modified field on .update?

Related issue where this scenario was brought up: #21, #451

My response bringing it up again: https://github.com/MongoEngine/mongoengine/issues/451#issuecomment-414149971

To my knowledge (please correct me if I'm mistaken!) the signal patterns only work with .save(). In the project I'm working on, we use .update and QuerySet's .update_one in various locations. My intuition is that these would would trigger a signal?

(To my knowledge, we don't have update hooks in Django ORM either, in favor of auto_now/auto_now_add, per discussion in #21): https://code.djangoproject.com/ticket/21461

Assuming this doesn't happen - is there a canonical way to have a updated/updated_at/modified/modified_at field update with .update without overriding the method on the document?

Other things:

• Examples in mongoengine documentation: http://docs.mongoengine.org/guide/signals.html#attaching-events (to my knowledge, this would only work if using .save()? So a codebase could potentially be missing modified changes?)
• StackOverflow question: https://stackoverflow.com/q/8098122

Start by reading the signal documentation linked in the issue and the QuerySet .update and .update_one entry points, then compare their behavior with .save(). The issue names no specific files or tests; done would require a decided, testable approach for updating modified fields during these operations.