#21169: Deletion in custom reverse managers
-------------------------------------+-------------------------------------
Reporter: sebastian | Owner: loic84
Type: Bug | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Release blocker | Triage Stage: Accepted
Keywords: | Needs documentation: 1
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by loic84):
* needs_docs: 0 => 1
* has_patch: 0 => 1
Comment:
For the record I'm going to list all the changes and issues addressed by
this ticket and #21174 since they are related.
The culprits: the `clear()` and `remove()` methods of the M2M, FK, and GFK
related managers, so six methods in total.
Issues:
- All methods except `FK.clear()` completely bypassed default filtering
(i.e. custom `Manager.get_queryset()` with filters).
- All methods except `FK.clear()` caused multiple consecutive db
operations run without transaction. (see #21174)
- Inconsistency between the implementation of `FK.remove()` and
`FK.clear()`, in particular wrt emitted signals.
- `M2M.clean()` and `M2M.remove()` were prone to race conditions for
symmetrical relations. (see #comment:8)
List of changes:
- All methods now respect default filtering, which means you can't delete
or change something that is filtered out.
- All methods now run in a single query, which addresses all transaction
concerns.
- `FK.remove()` changed from successive `save()` calls, to a single
`update()`.
Gotcha: `pre_save` and `post_save` signals aren't fired anymore.
- `M2M.remove()` and `M2M.clear()` rely on subqueries when filtering is
involved.
- Symmetrical `M2M.remove()` and `M2M.clear()` now run in a single query.
- `GFK.remove()` and `GFK.clear()` now perform bulk delete.
Gotcha: `Model.delete()` is not called anymore.
--
Ticket URL: <https://code.djangoproject.com/ticket/21169#comment:9>
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