#17688: No m2m_changed signal sent to when referenced object is deleted
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Reporter: jblaine@… | Owner:
| jorgecarleitao
Type: Bug | Status: assigned
Component: Database layer | Version: 1.3
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by Gary Chen):
Interested in taking on this change. I'm thinking it'll involve:
* Undoing [26c4be2ebe] to disable fast_deletes when m2m_changed signals
are connected
* Took at look at [https://github.com/django/django/pull/6579] but I'm not
sure the approach there is correct, the hidden through model is already
included and cascaded in the collector. We just need to fire the correct
signal in that case, and we can do so easily by checking
`model._meta.auto_created`
[https://github.com/django/django/blob/a97d6b198eec13a98ef60d7f440528ba82889071/django/db/models/deletion.py#L327
which is already being done].
One question is if `model._meta.auto_created` is indeed a determiner for
if a model is a generated m2m through model--I'm assuming it's already
being used as such to skip pre/post_delete signals.
There is a design question I think whether the `m2m_changed` signal should
only be triggered explicitly via methods on ManyRelatedManager, or any
changes to the autogenerated m2m model should in fact be captured. I think
there's precedent with deletes at least, in that cascading deletes trigger
pre/post_delete signals. So it's not a far stretch that deleted m2m
relations trigger m2m_changed signals.
--
Ticket URL: <https://code.djangoproject.com/ticket/17688#comment:19>
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