[Django] #24793: Subtracting DateTime fields in a query expression should use timediff
Django
-------------------------------------+-------------------------------------
Reporter: sparkyb | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 1.8
(models, ORM) | Keywords: datetime duration
Severity: Normal | expression
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
If I have a model with start and end DateTime fields, I'd like to be able
to annotate a query with the duration. For instance, with the model
{{{
class Event(Model):
start_time = DateTimeField()
end_time = DateTimeField()
}}}
I want to be able to do the following query:
{{{Event.objects.annotate(duration=ExpressionWrapper(F('end_time')-F('start_time'),output_field=DurationField()))}}}.
However this yields and incorrect result. At least in MySQL, the proper
SQL is {{{timediff(end_time,start_time) as duration}}}. I have not found
an alternate way to do this with Django's ORM without writing SQL.
--
Ticket URL: <https://code.djangoproject.com/ticket/24793>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
-------------------------------------+-------------------------------------
Reporter: sparkyb | Owner: nobody
Component: Database layer | Version: 1.8
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: josh.smeaton@… (added)
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
* type: Uncategorized => New feature
* stage: Unreviewed => Accepted
Comment:
Backends that don't have native duration types (mysql and sqlite) do not
have support for `date - date` annotations. This is guarded by the
`has_native_duration_field` flag in tests.
You can implement your own expression that uses timediff though:
{{{
class TimeDiff(Func):
function = 'timediff'
output_field = TimeField()
# you could also implement __init__ to enforce only two date fields
Event.objects.annotate(duration=TimeDiff('end_time', 'start_time')
}}}
Note that I've made the output_field a TimeField rather than a
DurationField. MySQL returns Time as the result of `date-date`, not a
duration/interval.
Considering that adding/subtracting dates is relatively common, I wouldn't
mind seeing better support for mysql and sqlite if it's possible. So, I'm
accepting on that basis. If someone is able to provide a patch that makes
`F('date') - F('otherdate')` work consistently on all backends, then we'd
probably accept that.
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:1>
Django
-------------------------------------+-------------------------------------
Reporter: sparkyb | Owner: nobody
Component: Database layer | Version: 1.8
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by LegoStormtroopr):
@jarshwah
I've got a work around that I think works for SQLite using SQLites native
`julianday` function, and am keen to progress this as an actual solution,
but the code is a little dense for me.
Would you be able to point me in the direction of where the subtract
expressions are handled?
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:2>
Django
-------------------------------------+-------------------------------------
Reporter: sparkyb | Owner: nobody
Component: Database layer | Version: 1.8
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by jarshwah):
Hi Lego,
I'm really sorry I've taken so long to get back to you, I'll do better in
future.
Where I think you should be looking is
django.db.models.expression.CombinedExpression.as_sql() method.
You would put some handling in there to check left and right hand side for
two dates, and then we'd probably have some backend specific SQL that
knows how to handle date(+-)date.
If you look in the as_sql method you'll see how DurationExpressions are
handled. It's guarded by a feature flag (has_native_duration_field). You
might want to guard by another feature flag, something like
"supports_date_arithmetic". You could then create a DateExpression class
that handles the backend specific way of doing date math.
Hopefully that's enough information for you to get started. Please hit me
up if you need some help or clarification.
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:3>
Django
-------------------------------------+-------------------------------------
Reporter: sparkyb | Owner: nobody
Component: Database layer | Version: 1.8
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* cc: charettes (added)
Comment:
I tried to help someone on the user mailing list with
[https://groups.google.com/d/msg/django-users/xIP7hhp0WqQ/_ld98nL6EgAJ a
similar issue with time fields].
I came up with tests that shows that all but `DateField` combinations work
on PostgreSQL while all combinations fails on `SQLite3`:
{{{#!python
from django.db import models
class DateModel(models.Model):
start = models.DateField()
end = models.DateField()
class TimeModel(models.Model):
start = models.TimeField()
end = models.TimeField()
class DateTimeModel(models.Model):
start = models.DateTimeField()
end = models.DateTimeField()
}}}
{{{#!python
import datetime
from django.db.models import DurationField, ExpressionWrapper, F
from django.test import TestCase
from pytz import UTC
from . import models
class DurationTests(TestCase):
@classmethod
def setUpTestData(cls):
models.DateModel.objects.create(
start=datetime.date(2015, 5, 10),
end=datetime.date(2015, 5, 12),
)
models.TimeModel.objects.create(
start=datetime.time(10),
end=datetime.time(13, 30),
)
models.DateTimeModel.objects.create(
start=datetime.datetime(2015, 5, 10, 10, 00, tzinfo=UTC),
end=datetime.datetime(2015, 5, 12, 13, 30, tzinfo=UTC),
)
def test_timemodel(self):
self.assertEqual(
models.TimeModel.objects.annotate(duration=ExpressionWrapper(
F('end') - F('start'), output_field=DurationField()
)).get().duration, datetime.timedelta(hours=3, minutes=30)
)
def test_datemodel(self):
self.assertEqual(
models.DateModel.objects.annotate(duration=ExpressionWrapper(
F('end') - F('start'), output_field=DurationField()
)).get().duration, datetime.timedelta(days=2)
)
def test_datetimemodel(self):
self.assertEqual(
models.DateTimeModel.objects.annotate(duration=ExpressionWrapper(
F('end') - F('start'), output_field=DurationField()
)).get().duration, datetime.timedelta(days=2, hours=3,
minutes=30)
)
}}}
PostgreSQL failure:
{{{
======================================================================
FAIL: test_datemodel (duration_expression.tests.DurationTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/simon/workspace/ticketing/duration_expression/tests.py",
line 40, in test_datemodel
)).get().duration, timedelta(days=2)
AssertionError: 2 != datetime.timedelta(2)
----------------------------------------------------------------------
}}}
SQLite3 failures:
{{{
======================================================================
FAIL: test_datemodel (duration_expression.tests.DurationTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/simon/workspace/ticketing/duration_expression/tests.py",
line 37, in test_datemodel
)).get().duration, datetime.timedelta(days=2)
AssertionError: datetime.timedelta(0) != datetime.timedelta(2)
======================================================================
FAIL: test_datetimemodel (duration_expression.tests.DurationTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/simon/workspace/ticketing/duration_expression/tests.py",
line 44, in test_datetimemodel
)).get().duration, datetime.timedelta(days=2, hours=3, minutes=30)
AssertionError: datetime.timedelta(0) != datetime.timedelta(2, 12600)
======================================================================
FAIL: test_timemodel (duration_expression.tests.DurationTests)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/simon/workspace/ticketing/duration_expression/tests.py",
line 30, in test_timemodel
)).get().duration, datetime.timedelta(hours=3, minutes=30)
AssertionError: datetime.timedelta(0, 0, 3) != datetime.timedelta(0,
12600)
----------------------------------------------------------------------
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:4>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: assigned
Component: Database layer | Version: 1.8
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* status: new => assigned
* owner: nobody => charettes
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:5>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: assigned
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* has_patch: 0 => 1
Comment:
[https://github.com/django/django/pull/5997 PR]
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:6>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: assigned
(models, ORM) |
Keywords: datetime duration | Triage Stage: Accepted
expression |
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* needs_docs: 0 => 1
Comment:
Needs a mention in the release notes for third-party database backends.
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:7>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: assigned
(models, ORM) |
Severity: Normal | Resolution:
Keywords: datetime duration | Triage Stage: Accepted
expression |
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* needs_docs: 1 => 0
* version: 1.8 => master
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:8>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: assigned
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
expression | checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* stage: Accepted => Ready for checkin
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:9>
Django
-------------------------------------+-------------------------------------
Type: New feature | Status: closed
Component: Database layer | Version: master
(models, ORM) |
Keywords: datetime duration | Triage Stage: Ready for
expression | checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
* status: assigned => closed
* resolution: => fixed
Comment:
In [changeset:"766afc22a1dfa7d34a08de85356b7bc9dba025e7" 766afc22]:
{{{
#!CommitTicketReference repository=""
revision="766afc22a1dfa7d34a08de85356b7bc9dba025e7"
Fixed #24793 -- Unified temporal difference support.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:10>
Django
-------------------------------------+-------------------------------------
| Charette
Type: New feature | Status: closed
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution: fixed
Keywords: datetime duration | Triage Stage: Ready for
expression | checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Mariusz Felisiak <felisiak.mariusz@…>):
In [changeset:"088a6fab1ccd1efcd4ce28b353df3c03dcfa0caf" 088a6fa]:
{{{
#!CommitTicketReference repository=""
revision="088a6fab1ccd1efcd4ce28b353df3c03dcfa0caf"
Refs #24793 -- Removed bogus connection argument from
SQLCompiler.compile() calls.
The method doesn't expect a connection object to be passed as its second
argument.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/24793#comment:11>