id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
37454	Should DecimalField on postgresql adapt its values?	Julien Palard		"Currently the DecimalField values are not adapted:

{{{
     def adapt_decimalfield_value(self, value, max_digits=None, decimal_places=None):
        """"""
        Transform a decimal.Decimal value to an object compatible with what is
        expected by the backend driver for decimal (numeric) columns.
        """"""
        return value
}}}

Say I use:

{{{
    class Doh(models.Model):
        cost = models.DecimalField(""cost"", max_digits=9, decimal_places=3)
}}}

Then it behave surprisingly at request time:

{{{
$ ./manage.py shell
>>> from decimal import Decimal
>>> kwargs = {""cost"": Decimal(""12345.123456789"")}
>>> Doh.objects.create(**kwargs)
<Doh: Doh object (1)>
>>> Doh.objects.get(**kwargs)
Traceback (most recent call last):
[...]
app.models.Doh.DoesNotExist: Doh matching query does not exist.
}}}

So currently I'm using:

{{{
        with localcontext() as ctx:
            ctx.rounding = ROUND_UP
            kwargs = {""cost"": round(Decimal(""12345.123456789""), 3)}
}}}

But it feels fragile: what if I change the scale on the model side? I'll have to change all my calls to round.

Also it feels like implementing something that could be done in the adapter: if we know the decimal has only 3 places, allowing a request to touch the database with a WHERE with a value with more prevision will always result in no answer from the DB so there’s no point? Or am I missing something?"	Uncategorized	new	Database layer (models, ORM)	6.1	Normal			Julien Palard	Unreviewed	0	0	0	0	0	0