#25470: Serious performance impact (500x slower!) when querying distinct model
dates objects
-------------------------------------+-------------------------------------
Reporter: stanleyxu2005 | Owner: felixxm
Type: | Status: assigned
Cleanup/optimization |
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by felixxm):
* has_patch: 0 => 1
Comment:
I made [https://github.com/django/django/pull/5428 PR] to omit unnecessary
type cast.
In my opinion, the second step, is to change default {{{order}}} in
{{{dates}}}, {{{datetimes}}} methods
{{{#!diff
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -726,21 +726,25 @@ class QuerySet(object):
clone._iterable_class = FlatValuesListIterable if flat else
ValuesListIterable
return clone
- def dates(self, field_name, kind, order='ASC'):
+ def dates(self, field_name, kind, order=None):
"""
}}}
or give a way to disable it
{{{#!diff
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -733,14 +733,18 @@ class QuerySet(object):
"""
assert kind in ("year", "month", "day"), \
"'kind' must be one of 'year', 'month' or 'day'."
- assert order in ('ASC', 'DESC'), \
- "'order' must be either 'ASC' or 'DESC'."
- return self.annotate(
+ assert order is None or order in ('ASC', 'DESC'), \
+ "'order' must be either 'ASC', 'DESC' or None."
+ qs = self.annotate(
datefield=Date(field_name, kind),
plain_field=F(field_name)
).values_list(
'datefield', flat=True
- ).distinct().filter(plain_field__isnull=False).order_by(('-' if
order == 'DESC' else '') + 'datefield')
+ ).distinct().filter(plain_field__isnull=False)
+ if order is not None:
+ return qs.order_by(('-' if order == 'DESC' else '') +
'datefield')
+ else:
+ return qs
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25470#comment:14>
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