[Django] #28616: DISTINCT ON and update() does the wrong thing
Django
-------------------------------------+-------------------------------------
Reporter: Daniel | Owner: nobody
Keller |
Type: Bug | Status: new
Component: Database | Version: 1.11
layer (models, ORM) |
Severity: Normal | Keywords:
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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If I have a model like
{{{
from django.db import models
from django.utils import timezone
class Foo(models.Model):
num = models.IntegerField(default=0)
date = models.DateTimeField(default=timezone.now)
flag = models.BooleanField(default=False)
}}}
and (with Postgresql) I do
{{{
Foo.objects.order_by('num', '-date').distinct('num').only('pk')
}}}
I get a query like
{{{
SELECT DISTINCT ON ("app_foo"."num") "app_foo"."id" AS Col1 FROM "app_foo"
ORDER BY "app_foo"."num" ASC, "app_foo"."date" DESC; args=()
}}}
which returns the latest `Foo` for each `num`.
BUT, if I do
{{{
Foo.objects.order_by('num', '-date').distinct('num').update(flag=True)
}}}
then it executes
{{{
UPDATE "app_foo" SET "flag" = true; args=(True)
}}}
which updates ''everything''.
I don't necessarily think that this behaviour should be supported, but it
would be nice to at least get a `NotImplementedError`.
--
Ticket URL: <https://code.djangoproject.com/ticket/28616>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: new
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: felixxm (added)
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:1>
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: new
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* stage: Unreviewed => Accepted
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:2>
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: assigned
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* status: new => assigned
* owner: nobody => messfish
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:3>
Django
-------------------------------------+-------------------------------------
| Mishra
Type: Bug | Status: assigned
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* owner: nobody => Anvesh Mishra
* status: new => assigned
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:3>
Django
-------------------------------------+-------------------------------------
| Mishra
Type: Bug | Status: assigned
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Anvesh Mishra):
Should we add a support for this behavior or stick to
`NotImplementedError` ?
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:4>
Django
-------------------------------------+-------------------------------------
Type: Bug | Status: new
Component: Database layer | Version: 1.11
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: Anvesh Mishra (added)
* owner: Anvesh Mishra => (none)
* status: assigned => new
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:5>
Django
-------------------------------------+-------------------------------------
| Mishra
Type: Bug | Status: assigned
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* owner: (none) => Anvesh Mishra
* status: new => assigned
Comment:
On looking into it further it seems like the problem comes because of how
the `QuerySet.update()` works
{{{ #!python
query = self.query.chain(sql.UpdateQuery)
}}}
The Query.chain() changes the class of the current object to UpdateQuery
which removes the previous query as a new object is created i.e
{{{
SELECT DISTINCT ON ("distinct_foo"."num") "distinct_foo"."id",
"distinct_foo"."num", "distinct_foo"."date", "distinct_foo"."flag" FROM
"distinct_foo" ORDER BY "distinct_foo"."num" ASC, "distinct_foo"."date"
DESC
}}}
and then replaces it with
{{{
UPDATE "app_foo" SET "flag" = true; args=(True)
}}}
instead of combining both.
--
Ticket URL: <https://code.djangoproject.com/ticket/28616#comment:6>