#26430: Coalesce in Aggregations ignored when EmptyResultSet returned
-------------------------------------+-------------------------------------
Reporter: ryanprater | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.9
(models, ORM) | Keywords: aggregation coalesce in
Severity: Normal | queryset
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Using an empty list when using the `__in=` returns an EmptyResultSet and
prevents an Aggregate Coalesce from working properly. See below:
# Test with matched Queryset. Sum will return 50
{{{OrderItem.objects.filter(pk__in=[1]).aggregate(test=Coalesce(Sum('quantity'),
Value(0)))}}}
{{{>>>{'test': 50}}}}
# Test with unmatched Queryset. Sum will return 0
{{{OrderItem.objects.filter(pk__in=[-1]).aggregate(test=Coalesce(Sum('quantity'),
Value(0)))}}}
{{{>>> {'test':0}}}}
# Test with unmatched Queryset (using empty list). EmptyResultSet returned
because of empty list. Sum will return NONE
{{{OrderItem.objects.filter(pk__in=[]).aggregate(test=Coalesce(Sum('quantity'),
Value(0)))}}}
{{{>>> {'test': None}}}}
Simon Charette on django-users suggested the following:
''From what I understand the ORM simply doesn't perform any query in this
case
as the `pk__in` lookup cannot match any `OrderItem` and result in an
`EmptyResultSet` exception[1].''
''This exception is caught in the `Query.get_aggregation()` method where
all
aggregates are converted to `None`[2].''
''I suppose we should alter the `except EmptyResultSet` clause to account
for
`outer_query.annotation_select` items that are `Coalesce()` instances used
with
`Value()` but I'm unsure about how it should be done.''
[1]
https://github.com/django/django/blob/2e0cd26ffb29189add1e0435913fd1490f52b20d/django/db/models/lookups.py#L221-L223
[2]
https://github.com/django/django/blob/2e0cd26ffb29189add1e0435913fd1490f52b20d/django/db/models/sql/query.py#L439-L445
See full discussion here:
https://groups.google.com/forum/#!topic/django-users/HGD3Vv3IerA
--
Ticket URL: <https://code.djangoproject.com/ticket/26430>
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