#13666: Updates with F objects on decimal fields raise MySQL warnings
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Reporter: KyleMac | Owner: nobody
Status: reopened | Milestone:
Component: Documentation | Version: 1.2
Resolution: | Keywords:
Stage: Unreviewed | Has_patch: 0
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Comment (by KyleMac):
Assuming that the field "balance" is a decimal field with 2 decimal
places, in raw SQL the following will show the truncation warning:
{{{
UPDATE ticket SET balance = 10.00;
UPDATE ticket SET balance = balance - '1.79';
SHOW WARNINGS;
}}}
However, the following will work fine:
{{{
UPDATE ticket SET balance = 10.00;
UPDATE ticket SET balance = balance - 1.79;
SHOW WARNINGS;
}}}
It seems that MySQL doesn't like strings as much as it likes floats and
Django converts Decimal() to strings. So
{{{
Account.objects.create(name='z1', balance='10.00')
Account.objects.filter(name__startswith='z').update(balance=F('balance') -
Decimal('1.79'))
}}}
or
{{{
Account.objects.create(name='z1', balance='10.00')
Account.objects.filter(name__startswith='z').update(balance=F('balance') -
'1.79')
}}}
raise exceptions, but
{{{
Account.objects.create(name='z1', balance='10.00')
Account.objects.filter(name__startswith='z').update(balance=F('balance') -
float(Decimal('1.79')))
}}}
works fine.
--
Ticket URL: <http://code.djangoproject.com/ticket/13666#comment:3>
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