#33579: Raise a specialized exception when Model.save(update_fields) does not
affect any rows
-------------------------------------+-------------------------------------
Reporter: Simon | Owner: nobody
Charette |
Type: New | Status: new
feature |
Component: Database | Version: 4.0
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
When `Model.save(update_fields)` is used to update an instance of a
previously fetched model and the resulting `UPDATE` doesn't affect any row
a `DatabaseError`
[https://github.com/django/django/blob/3b3f38b3b09b0f2373e51406ecb8c9c45d36aebc/django/db/models/base.py#L1000
is raised].
Since the resulting exception cannot be differentiated by its `type` from
any other exception raised during `save` (e.g. a failed `UPDATE` also
results in a `DatabaseError`) the only pattern to gracefully handle this
rare edge case to catch all `DatabaseError` and compare its `.args[0]` (or
`str` representation) to a string that doesn't offer any stability
guarantees.
In order to make it easier for advanced users that rely on the
`update_fields` feature to handle this case differently from others where
a `DatabaseError` is raised I propose that that we introduced a new
`DatabaseError` subclass that would be raised instead when an unexpected
empty update occurs.
I believe
[https://github.com/django/django/blob/3b3f38b3b09b0f2373e51406ecb8c9c45d36aebc/django/db/models/base.py#L997-L1000
both instances] should be switched to this pattern (`force_update` and
`update_fields`).
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Ticket URL: <https://code.djangoproject.com/ticket/33579>
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