#26433: Bug: annotating using When(id__in=[], ...) returns empty queryset
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Reporter: kevinmarsh | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.9
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by akaariai):
* needs_better_patch: => 0
* needs_docs: => 0
* needs_tests: => 0
* stage: Unreviewed => Accepted
Comment:
This is close to the problem mentioned in #26430. Here Case.as_sql() could
just catch the EmptyResultSet and instead return sql "1 = 0". But I wonder
if we are able to avoid the EmptyResultSet completely by the following
approach.
1. Instead of raising EmptyResultSet we generate sql, params = "1 = %s",
(EMPTY_PARAM,).
2. EMPTY_PARAM is converted to 0 when the SQL is executed.
3. When generating the SQL for a queryset which isn't a subquery of
another queryset, we check for existence of EMPTY_PARAM in the params
generated for the where clause. If one is found, we know we don't need to
execute the queryset at all.
4. In all other cases we run the query with the empty param. The condition
is always going to fail in the generated SQL, but that is exactly what we
want for this ticket.
This should also solve #26430 by the "isn't a subquery" condition in rule
3.
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Ticket URL: <https://code.djangoproject.com/ticket/26433#comment:1>
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