#36344: Accessing a related field after using defer() or only() unexpectedly
overwrites unsaved state on model instances
-------------------------------------+-------------------------------------
Reporter: Erick | Owner: (none)
Type: Uncategorized | Status: closed
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Simon Charette):
Accessing deferred fields in `__init__` is going to cause you a lot of
trouble #22858, #31435, #32660 and
[https://docs.djangoproject.com/en/5.2/ref/models/instances/#django.db.models.Model
is documented to be problematic].
It causes a silent N+1 query which explains why your value is overriden
when `value` is not part of the inclusion mask (accessing `self.value`
will cause it to be retrieved it from the database and then assigned on
the model instance).
If you ''really need'' to implement field retrieval in `__init__` you
should
[https://docs.djangoproject.com/en/5.2/ref/models/instances/#django.db.models.Model.get_deferred_fields
gate these retrieval behind get_deferred_fields].
{{{#!python
def __init__(self, *args, **kwargs):
super().__init__(self, *args, **kwargs)
if "value" not in self.get_deferred_fields():
self.value
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/36344#comment:3>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion visit
https://groups.google.com/d/msgid/django-updates/010701965dc04a65-4147fa60-4dc5-429a-b45e-94d0f68bc859-000000%40eu-central-1.amazonses.com.
