#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) |
Severity: Normal | Resolution:
Keywords: oracle | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by owais):
I am continuing work on this as part of
https://github.com/django/django/pull/5904. My intention is to only
support backends that actually support this feature i.e, Postgresql using
`RETURNING` and Oracle using `RETURNING INTO`. I can follow up with
another PR to "simulate" the behavior on backends that don't support it.
I've yet to write any docs or test cases.
The changes introduce 3 new field options.
== `return_on_insert` ==
When set to `True`, django will load the value from the database column
along with the insert statement and set it on the model. This is a noop on
mysql and sqlite.
== `return_on_update` ==
When set to `True`, django will load the value from the database column
along with the update statement and set it on the model. This is a noop on
mysql and sqlite.
== `delegated` ==
When set to `True`, django completely skips this field from insert and
update operations and let's the database set a value. It also sets
`return_on_update` and `return_on_insert` to `True` if no explicit value
is passed for them.
I think the combination of these three options covers almost every option
except when all the fields are delegated. In this case, the update
statement is never executed as `UPDATE` statement does not work without
`SET` clause and we can't intelligently decide whether to use the existing
value in update or not.
One possible way to reduce the impact of edge case would be to add another
field called `delegate_if_None` which would delegate the field to database
only when current value of the field is set to None. I'm not sure if such
a rare case should be supported though. It can easily by solved by setting
`return_on_insert` and `return_on_update` to True and then setting default
value or adding logic in database triggers.
--
Ticket URL: <https://code.djangoproject.com/ticket/21454#comment:20>
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