[Django] #35910: Use violation_error_message on UniqueContraint when only fields and no constraint is provided

[Django]

#35910: Use violation_error_message on UniqueContraint when only fields and no
constraint is provided
-------------------------------------+-------------------------------------
Reporter: James Walters | Type: New
| feature
Status: new | Component: Database
| layer (models, ORM)
Version: | Severity: Normal
Keywords: forms, models, | Triage Stage:
unique constraints | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
I have a model with the following UniqueConstraint:

{{{
models.UniqueConstraint(
fields=["client", "location", "description", "affects_all_locations"],
name="unique_desc_per_location_per_client",
violation_error_message="A closure with this description already exists
for this location (or all locations).",
)
}}}

Instead of seeing the error message I provided, I get "Closure with this
Client, Location, Description and Affects all locations already exists."
Upon consulting the
[https://docs.djangoproject.com/en/5.1/ref/models/constraints/#id3
documentation], I see that this is actually the intended behavior:

This message is not used for UniqueConstraints with fields and
without a condition. Such UniqueConstraints show the same message as
constraints defined
with Field.unique or in Meta.unique_together.

The default error message, however, gives the names of model fields that
users know nothing about, and the message I'm trying to provide gives the
user a better explanation about what's going on. Currently, I would have
to override the form's own validation to show this error message. However,
I don't think this should be necessary, given that I can provide a
violation_error_message straight to the UniqueConstraint.

I'm filing this under models/ORM since this is specifically related to
model validation, though reclassify it as Forms if that turns out to be
more appropriate.

If we decide we want to go in this direction, I'm open to working on a
patch, but I'll wait to see if we agree that this behavior should be
changed.
--
Ticket URL: <https://code.djangoproject.com/ticket/35910>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

[Django]

#35910: Use violation_error_message on UniqueContraint when only fields and no
constraint is provided
-------------------------------------+-------------------------------------

Reporter: James Walters | Owner: (none)
Type: New feature | Status: closed
Component: Database layer | Version:
(models, ORM) |
Severity: Normal | Resolution: duplicate

Keywords: forms, models, | Triage Stage:
unique constraints | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by Simon Charette):

* resolution: => duplicate
* status: new => closed

Comment:

I think you ran into #35103 which was recently fixed by
e970bb7ca71c00594b42a024a15a8ac007cc2c7a and will be part of Django 5.2.

You can try it out against `main` and
[https://docs.djangoproject.com/en/dev/ref/models/constraints/#id2 refer
to the updated documentation] in the mean time.

> In older versions, the provided `UniqueConstraint.violation_error_code`
was not used when `UniqueConstraint.fields` was set without a
`UniqueConstraint.condition`.

Please re-open if you believe you are running into a different issue.
--
Ticket URL: <https://code.djangoproject.com/ticket/35910#comment:1>

[Django]

#35910: Use violation_error_message on UniqueContraint when only fields and no
constraint is provided
-------------------------------------+-------------------------------------
Reporter: James Walters | Owner: (none)
Type: New feature | Status: closed
Component: Database layer | Version:
(models, ORM) |
Severity: Normal | Resolution: duplicate
Keywords: forms, models, | Triage Stage:
unique constraints | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Comment (by James Walters):

Ah! This would be it. Sorry, looked to see if someone had already ran into
this but didn't come across that ticket. Happy to see it fixed!
--
Ticket URL: <https://code.djangoproject.com/ticket/35910#comment:2>