#13666: Updates with F objects on decimal fields raise MySQL warnings
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Reporter: KyleMac | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.7
(models, ORM) |
Severity: Normal | 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 jarshwah):
Wouldn't it make sense to pass the number verbatim rather than
stringifying it? Or could that introduce inconsistencies with floats being
imprecise? What about the other backends, do they all accept string-like
decimal numbers and happily call them decimals?
If we want to go with a wrapping type though, it should be possible (from
1.8/master) to provide an `as_mysql()` for the Value expression.
Something like:
{{{
class Value(..):
def as_mysql(self, compiler, connection):
if self.output_field.get_internal_type() == 'DecimalField':
c = Cast(self, self.output_field)
return compiler.compile(c)
}}}
Where the `Cast` type above would need to be implemented in some way. The
implementation could be thorough and apply to all backends (quite a bit of
work), or it could be extremely simple, and only work for Decimal types on
MySQL. There's similar logic for Oracle with the `Coalesce` type and
conversions to NCLOB.
I'd be wary about providing the digits and precision arguments to the CAST
if they aren't exactly needed. If they can be avoided, then do so. Because
there's no nice way (currently) to pass that information.
--
Ticket URL: <https://code.djangoproject.com/ticket/13666#comment:13>
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