#22296: Documentation clarification: m2m_changed pk_set inconsistent between
post_add and post_remove
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Reporter: anentropic | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.5
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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the docs say:
"`pk_set`: For the pre_add, post_add, pre_remove and post_remove actions,
this is a set of primary key values that have been added to or removed
from the relation."
What I found is that for `action=='post_add'`:
- first time `add(x)` -> `set([x])`
- next time (same `x`) `add(x)` -> `set([])`
but for `action=='post_remove'`:
- first time `remove(x)` -> `set([x])`
- next time (same `x`) `remove(x)` -> `set([x])`
I feel like they should be consistent. Either way is fine but the
behaviour of `post_add` seems more useful to me (can avoid unnecessary
action in your signal receiver)... but it should be documented that you
get empty set if nothing needed adding.
I've only tried on 1.5 so far but looking at source I don't see any new
code to change this behaviour
https://github.com/django/django/blob/master/django/db/models/fields/related.py#L1032
Whereas it looks like the add method has code to deliberately exclude
already added items
https://github.com/django/django/blob/master/django/db/models/fields/related.py#L1008
I'm happy to make a patch if it's felt this is useful?
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Ticket URL: <https://code.djangoproject.com/ticket/22296>
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