#35269: GeneratedFields can't be defined on RelatedFields
-------------------------------------+-------------------------------------
Reporter: Perrine L. | Owner: nobody
Type: New feature | Status: closed
Component: Database layer | Version: 5.0
(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
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Comment (by Simon Charette):
You don't need any `GeneratedField` subclass to achieve what you're after,
simply use `ForeignObject` which is the accessor base of `ForeignKey`.
{{{#!python
from django.db.models.fields.related_fields import ForeignObject
class Event(models.Model):
last_updated_by_id = models.GeneratedField(
expression=Greatest("created_by", "confirmed_by", "canceled_by"),
output_field=models.BigIntegerField(),
db_index=True,
db_persist=True,
)
last_updated_by = ForeignObject(
User,
models.SET_NULL,
from_fields=["last_updated_by_id"],
to_fields=["id"],
related_name="last_updated_events_set",
null=True,
)
}}}
I also believe there is no reason to add this feature in core as with
these two primitives it should be trivial to implement a
`ForeignGeneratedField(ForeignObject)` that does exactly what you're after
in a third-party application for the rare use case this is useful.
--
Ticket URL: <https://code.djangoproject.com/ticket/35269#comment:7>
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