Re: [Django] #36133: Passing expression with wrongly attributed text output_field to Concat crashes on Postgres due the lack of casting

[Django]

#36133: Passing expression with wrongly attributed text output_field to Concat
crashes on Postgres due the lack of casting
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Reporter: Siburg | Owner: (none)
Type: Bug | Status: closed
Component: Database layer | Version: 5.1
(models, ORM) |
Severity: Normal | Resolution: invalid
Keywords: Cast, | Triage Stage:
ExpressionWrapper | 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 Siburg):

Thank you. I'm using PostgreSQL 14 and psycopg == 3.2.4 . Just tried it
out and the test passes with SQLite, so it is indeed a PostgreSQL thing.

I appreciate your simplification of removing the `ExpressionWrapper`
altogether. Happy to confirm that indeed works, and will adopt that in my
code.

But, still surprised by the unexpected breakage in Django 5.1. I naively
expected that specifying `output_field=models.CharField()` for an
`ExpressionWrapper` would lead to the intended result. I think that is the
gist of https://code.djangoproject.com/ticket/26650 as well. So it's
annoying that such a specification is useless, and the `ExpressionWrapper`
will provide a `bigint` anyway. Perhaps it would be good to clarify the
documentation in
https://docs.djangoproject.com/en/5.1/ref/models/expressions/#output-
field.

Thinking a little more about it, I realize that `output_field` is a very
trick thing and can depend on the database. For example, I am aware from
painful experience that SQLite causes problems with `DecimalField`. So I
don't have any clear solution myself for this breakage in 5.1.
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Ticket URL: <https://code.djangoproject.com/ticket/36133#comment:6>
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