#21461: Add pre_update and post_update signals
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Reporter: loic84 | Owner: loic84
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Normal | Triage Stage:
Keywords: | Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by akaariai):
The latest solution is close to what charettes suggested in comment:3. The
biggest distinctions are that pre_update is given the to-be updated
queryset instead of to-be-updated queryset.filter(pk_in=pk_set), and for
post_update you don't get queryset, you just get pk_set.
The reason for going with pk_set is that in some cases the only thing you
need is the set of primary keys, and if that happens to be a large set,
then doing pk_in=pk_set query will be expensive (PostgreSQL doesn't like
this type of query at all, and SQLite will not even execute a query with
more than 1000 pk values.
A possible solution is to provide both the queryset (with pk_in=pk_set
filtering pre-applied), *and* the pk_set to pre_/post_ update signals.
That way the user has nice API if that is all that is needed, but can also
just use the pk_set if that is possible.
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Ticket URL: <https://code.djangoproject.com/ticket/21461#comment:7>
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