#34160: Django 4.1 Expression contains mixed types for (Big/Small)IntegerFields.
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Reporter: Martin Lehoux | Owner: Martin
| Lehoux
Type: Bug | Status: assigned
Component: Database layer | Version: 4.1
(models, ORM) |
Severity: Release blocker | Resolution:
Keywords: | Triage Stage: Accepted
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):
What I believe is happening here is that `F("inventory_count") + Value(1)`
has its `output_field` resolved to `IntegerField` because it's the common
base of `inventory_count` (which I assume is a `SmallIntegerField` since
the models were not provided).
While `CombinedExpression._resolve_output_field` resolving logic deals
with subclassing properly `BaseExpression._resolve_output_field`
[https://github.com/django/django/blob/2848e5d0ce5cf3c31fe87525536093b21d570f69/django/db/models/expressions.py#L327-L329
isn't smart enough] to resolve a mix of `IntegerField` subclasses to the
largest denominator.
The three ways we could be fixing that would be:
1. Document this requirement the usage of explicit `output_field` either
to `Value` [https://docs.djangoproject.com/en/4.1/releases/3.2/ beyond the
3.2 release notes].
2. Make `Value._resolve_field` use different kind of `IntegerField`
subclasses when dealing with smaller/larger values. This could have the
unintended side effect of surfacing even more errors for mixed type as
`Value(n < 255)` would resolve to `SmallIntegerField` so I think this is
a bad idea.
3. Actually make `BasExpression._resolve_output_field` smarter with the
deprecation period it requires.
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Ticket URL: <https://code.djangoproject.com/ticket/34160#comment:10>
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