#35459: Case.extra is undocumented, untested, and can hide potential issues
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Reporter: Baptiste Mispelon | Owner: Priyank
Type: | Panchal
Cleanup/optimization | Status: assigned
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Comment (by Jacob Walls):
After looking more at the history, I'm nervous about removing `**extra`
from `Case` and/or `Subquery`/`Exists` given how close it is to the
documented pattern for `Func`. In particular, we have an
[https://docs.djangoproject.com/en/6.0/ref/models/expressions/#writing-
your-own-query-expressions example] of rewriting `Coalesce` from scratch
that inherits from `Expression` rather than `Func`, and it follows the
`Func`-style dynamic provision of `template`. The way
`Case`/`Subquery`/`Exists` allow dynamic templates feels like dogfooding
our own example.
> (Currently, template is pulled from extra:
template_params.get("template", self.template) in as_sql().) I'm not sure
if it's useful.
A [https://github.com/django/django/pull/6302/files#r56357943 similar
question] was asked at the time, and the answer was, at least for `Func`
subclasses, it could be useful. I'm worried saying it's useful for `Func`
subclasses but not `Exists` is a hyperfine distinction. (A `Subquery`
subclass might also want to specialize the template per backend, but
accept a generic parameter for all backends in `as_sql`, like `Cast`
does.)
Given that, my preference would be to close this ticket via documentation
and tests, but with improving the example (perhaps using a `CustomExists`
expression that is factored like `Cast`, e.g. it has vendor-specific
templates all relying on a single parameter accepted from `as_sql()`).
--
Ticket URL: <https://code.djangoproject.com/ticket/35459#comment:18>
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