id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34733	m2m_changed signal is unaware if .set() method is being called	Leif Kjos	Leif Kjos	"When a `related_m2m_field.set()` method is called, the `m2m_changed` signal is fired four times for action: `pre_remove`, `post_remove`, `pre_add`, and `post_add` (or `pre_clear` / `post_clear`). 

This poses a problem if the signal is supposed to run validation on the final state of the model. For example, let's say I have a model called `Customer` with a many-to-many relation to `SubscriptionPlan` and I have a `m2m_changed` signal that is supposed to validate if their SubscriptionPlan is valid.

If I call `Customer.subscription_plans.set([some_plans])`, the many-to-many manager will first call `subscription_plans.remove()` then `.add()` inside an atomic transaction. If my signal validates on the first `.remove()`, it could be in an invalid state, even though it won't be by the time the `.add()` completes. However, I still need to be able to validate on the signal if the standard `.remove()` method is called.

To get around this, I had to create a custom ManyToManyField with a custom RelatedManager that set an instance variable on the model when the `.set()` method was called. I'd like to propose adding a feature to the RelatedManager or to the signals to make the `m2m_changed` signal aware of if the `.set()` method was called when running. This could be a private attribute on the instance or extra information passed to the signal receiver. 

If this feature already exists or there's a decent workaround, let me know and i'll close the ticket! Otherwise, I have a patch in mind that I can raise a PR for and attach."	New feature	closed	Database layer (models, ORM)	dev	Normal	wontfix			Unreviewed	0	0	0	0	0	0