#27980: ExpressionWrapper is maybe masking a NotImplementedError on SQLite
-------------------------------------+-------------------------------------
Reporter: | Owner: nobody
denisroldan |
Type: Bug | Status: new
Component: Database | Version: 1.10
layer (models, ORM) | Keywords: db, orm, sqlite,
Severity: Normal | datetime, NotImplementedError
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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Hello folks!
The new ExpressionWrapper is maybe masking some NotImplementedErrors.
Here's an example:
Under Django 1.10 & Python 3.6:
If I try
{{{
tasks = Task.objects.all()
tasks.annotate(time_elapsed=Sum(F('resolution_date')-F('request_date'),
output_field=DateTimeField())).aggregate(Avg('time_elapsed'))
}}}
Falls correctly into:
{{{
NotImplementedError: You cannot use Sum, Avg, StdDev, and Variance
aggregations on date/time fields in sqlite3 since date/time is saved as
text.
}}}
Of course, if I change into Postgre all runs smoothly. Unfortunately if I
use the brand new ExpressionWrapper I don't get any exception raised:
{{{
from django.db.models import ExpressionWrapper, F, DurationField, Avg
tasks = Task.objects.all()
duration = ExpressionWrapper(F('resolution_date') - F('request_date'),
output_field=DurationField())
tasks.annotate(time_elapsed=duration).aggregate(Avg('time_elapsed'))
{'time_elapsed__avg': None}
}}}
Under postgre and MySQL I can get that value and, of course, is not None.
And, by the way, you can do this:
{{{
tasks.annotate(time_elapsed=duration)[0].time_elapsed
datetime.timedelta(16, 74471, 878000)
}}}
So maybe it's a bug of the Avg Implementation when using a
ExpressionWrapper or maybe the exception is masked as None.
--
Ticket URL: <https://code.djangoproject.com/ticket/27980>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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