#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 fero):
Hello Sarah,
thanks for the answer
Replying to [comment:4 Sarah Boyce]:
> Hi Perrine,
Perrine?!? Sorry...I think you are answering me, and not Perrine. I hope
to be right.
> this ticket should only be re-opened if you do as Mariusz requested and
provide a valid column DDL definition that you believe is not currently
supported.
I have opened the issue without a DDL because the matter is just a way on
how Django give an accessor to ForeignKey attributes, mainly very useful
lookup. And this can be done (at least in PostgreSQL) even without
constraints. So no DDL really required for this feature.
> I believe this will not be possible as
[https://www.postgresql.org/docs/current/ddl-generated-columns.html the
linked documentation states] and Mariusz mentioned, `GeneratedFields`
cannot reference anything other than the current row in **any way** and
being a `ForeignKey` is a reference to an external model.
Yes, the GeneratedField can reference only info of its own row. I have had
the problem when I wanted to created a generated field with a CASE WHEN
and apply a Now(), aka CURRENT_TIMESTAMP as a default value. This cannot
be done.
But in this case the ForeignKey is just and ID and it is computed from
data of its own row. It is really the same as a BigIntegerField (or a
CharField if you use id like ssn), but it gives you a quicker way to
access to the related model.
So, I really appreciate your answer, but my humble opinion disagrees with
the position that implementing this feature would imply that
GeneratedField relies in external data.
> Thank you for the sample project and I can see what you're trying to do.
As what you're suggesting would be a new feature to Django, the
recommended path forward is to first propose and discuss the idea with the
community and gain consensus that this would be a desirable addition to
Django. To do that, please consider starting a new conversation on the
[https://forum.djangoproject.com/c/internals/5 Django Forum], where you'll
reach a wider audience and likely get extra feedback.
>
> I'll close this ticket, but if there is a community agreement for the
feature request, you are welcome to create a ticket for the new feature
and point to the forum topic. For more details, please see
[https://docs.djangoproject.com/en/stable/internals/contributing/bugs-and-
features/#requesting-features the documented guidelines for requesting
features].
>
I leave the ticket closed, but I have answered here to return you with a
feedback, and to link the ticket in the forum where I will go.
Thank you very much!
--
Ticket URL: <https://code.djangoproject.com/ticket/35269#comment:6>
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