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Fixed #35559 -- Avoided unnecessary query on sliced union of empty queries.

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While refs #34125 focused on the SQL correctness of slicing of union of
potentially empty queries it missed an optimization opportunity to avoid
performing a query at all when all queries are empty.

Thanks Lucidiot for the report.
This commit is contained in:
Simon Charette
2024-06-25 23:39:23 -04:00
committed by Sarah Boyce
parent 6b3f55446f
commit 9cb8baa0c4
2 changed files with 44 additions and 34 deletions
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6
tests/queries/test_qs_combinators.py
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@@ -76,6 +76,12 @@ class QuerySetSetOperationTests(TestCase):
qs3 = qs1.union(qs2)
self.assertNumbersEqual(qs3[:1], [0])
def test_union_all_none_slice(self):
qs = Number.objects.filter(id__in=[])
with self.assertNumQueries(0):
self.assertSequenceEqual(qs.union(qs), [])
self.assertSequenceEqual(qs.union(qs)[0:0], [])
def test_union_empty_filter_slice(self):
qs1 = Number.objects.filter(num__lte=0)
qs2 = Number.objects.filter(pk__in=[])