#28915: Regression in value of DecimalFields on SQLite in Django 2.0
-------------------------------------+-------------------------------------
Reporter: Raphael | Owner: nobody
Michel |
Type: Bug | Status: new
Component: Database | Version: 2.0
layer (models, ORM) |
Severity: Release | Keywords:
blocker |
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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With Django 1.11, when reading the value of a DecimalField from the
database, the Decimal is always returned with the precision of the
DecimalField, i.e. if the field has 2 decimal places, I always get a
Decimal with two decimal places as well.
With Django 2.0, I get a rounded decimal with no more decimal places.
Sample:
{{{
obj = Foo.objects.create(a="bar", d=Decimal('8.320'))
obj.refresh_from_db()
print(repr(obj.d))
}}}
This will output `Decimal('8.320')` on Django 1.11 but `Decimal('8.32')`
on Django 2.0.
For me (and likely many others) this is quite critical: For example, if
you use DecimalFields to store amounts of money in a currency that always
has two places, you can just pass the databases to `localize()` and get a
user-friendly representation. This is no longer possible, as you would
first need to call quantize in every single place which would be quite an
effort to do in a large codebasis.
Since there is no mention of this in the release notes, I believe this is
an unwanted regression and hope it can be fixed in 2.0.2 or the like.
I wrote a
[https://github.com/raphaelm/django/commit/6c682b619e88f69e4c75b890f8c3eed8fcd1aa87
regression test] for the problem and ran `git bisect` to identify that the
problem was introduced in commit
[https://github.com/django/django/commit/a146b65628e702a9a3ed5be21542ca45366fbb29
a146b6562].
I did not find a way to keep the performance gain of this commit without
introducing this regression, so I strongly ask to revert that commit
altogether for now (and add my regression test, if wanted) until someone
has a better idea how to optimize this.
--
Ticket URL: <https://code.djangoproject.com/ticket/28915>
Django <https://code.djangoproject.com/>
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