#18306: Deferred models should automatically issue update_fields when saving
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Reporter: akaariai | Owner: akaariai
Type: | Status: new
Cleanup/optimization | Version: master
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: | Patch needs improvement: 1
Has patch: 1 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Changes (by akaariai):
* needs_better_patch: 0 => 1
Comment:
I spotted two issues:
1. When doing a deferred model .save() with using argument, where the
using is to other database than where the object was fetched, the
"update_fields" machinery should not be used. This is a minor corner case,
but should still work.
2. The "deferred fields" is remembered in instance._meta, and it is
altered when a field is set to a value - this results in changing the
"deferred fields" property for _all_ instances, not just for the instance
which was changed. This is a blocker issue.
I see two ways forward:
- remember the loaded fields (instead of deferred fields) in
instance._state instead of instance._meta.
- do not remember the deferred fields at all. Instead check just for
instance._deferred. If set, then go through all fields and check if any of
the fields are instances of !DeferredAttribute. Those fields which are
instances of !DeferredAttribute are the deferred fields.
The second approach should be very robust, and I think it should be used.
The check to use is:
{{{
for field in self._meta.fields:
if isinstance(self.__class__.__dict__.get(field.attname),
DeferredAttribute):
# add to deferred fields.
}}}
See: https://github.com/akaariai/django/tree/ticket_18306 for details.
There are also some other added tests.
I stumbled upon other issues while working on this ticket, see
https://github.com/akaariai/django/tree/defer_inheritance_pk, #18343. Some
(well at least one) of the added tests need this work to pass.
--
Ticket URL: <https://code.djangoproject.com/ticket/18306#comment:7>
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