#21454: Ignoring certain fields on INSERT and UPDATE queries
-------------------------------------+-------------------------------------
Reporter: mpessas | Owner: mpessas
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 0
Has patch: 1 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by mpessas):
Replying to [comment:3 mpessas]:
> Replying to [comment:2 akaariai]:
> > It would be really useful to do autorefresh after save. Access to
database set values could also be done with RETURNING, but for first
implementation just executing a query from .save() would be enough.
>
> I would rather avoid the extra query to re-read the db-default values;
it would have a significant impact on performance, when one of the goals
was to improve performance in the first place.
>
> Regarding the `RETURNING` clause, it is not part of the SQL standard
AFAIK (see http://www.postgresql.org/docs/9.1/static/sql-
update.html#AEN76402) and that's the reason I avoided it. That said, can
we have backend-specific codepaths in Django? That is, use the `RETURNING`
clause, when available, and fallback to a re-read query otherwise.
>
> In any case, I suppose we should allow the developer to skip the re-read
query, if using the `RETURNING` clause is not possible. How does that
sound?
>
Check commit
https://github.com/mpessas/django/commit/dac93937c66040cb901e5e48bd6deba5ce51de9e.
If the backend supports the RETURNING clause, we use that to fetch the
values the database has given to the db-default fields. Otherwise, an
extra SELECT query is issued. If the user does not want this overhead, he
can set `force_fetch=False` (which is the default).
There are two main issues here: I have not checked yet how this works,
when Model inheritance is used and the Oracle backend is broken.
Regarding the latter, I have not found any helpful docs about the
RETURNING clause and I cannot test it either. Is there someone I could ask
or should I contact the cx_oracle developers directly?
--
Ticket URL: <https://code.djangoproject.com/ticket/21454#comment:4>
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