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
15766	select_related() changes type of DecimalField	Carsten Fuchs	nobody	"As originally reported at http://groups.google.com/group/django-users/browse_thread/thread/f797684ef2670ed2:

Using Django 1.3 with Python 2.6.5 on Ubuntu 10.04 and mod_wsgi, with Oracle database, I've just experienced a case where the use of select_related() changes the result type of a DecimalField in a related object from decimal.Decimal to float (which in turn breaks my application).


In detail, please consider the following models (unrelated fields omitted for clarity):

{{{
#!python
class Code(models.Model):
    id        = models.BigIntegerField(primary_key=True)
    grenzwert = models.DecimalField(null=True, max_digits=5, decimal_places=2, blank=True)

class Erfasst(models.Model):
    id   = models.AutoField(primary_key=True)
    code = models.ForeignKey(Code, db_column='code')
}}}

And the following shell session:

{{{
lori@keep-surfing:~/Zeiterfassung$ python manage.py shell
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type ""help"", ""copyright"", ""credits"" or ""license"" for more information.
(InteractiveConsole)
>>> from Zeiterfassung.Lori.models import *

>>> z = Erfasst.objects.get(id=2726498)
>>> z.code.grenzwert
Decimal('10.00')
>>> type(z.code.grenzwert)
<class 'decimal.Decimal'>
>>> z.code.grenzwert > Decimal(0)
True

>>> z = Erfasst.objects.select_related().get(id=2726498)
>>> z.code.grenzwert
10.0
>>> type(z.code.grenzwert)
<type 'float'>
>>> z.code.grenzwert > Decimal(0)
False
}}}

(The last line is the one that caused/causes the problems in my app...)

In the second part of the example with select_related(), I'd have expected that it returns type decimal.Decimal as in the first.

Python 2.7 seems to handle Decimal-float comparisons differently/better than 2.6, and the above would probably silently work with Python 2.7, but not 2.6.
"	Bug	closed	Database layer (models, ORM)	1.3	Normal	worksforme			Unreviewed	0	0	0	0	0	0