#23797: SQL generated for negated F() expressions is incorrect
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Reporter: mssnlayam | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.7
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by akaariai):
Yes, .exclude() should be the complement of .filter(). As said in
comment:2 the `WHERE (length = width)) IS NOT true` way is just way too
slow at least on PostgreSQL (always a sequential scan according to my
tests). Going for the NOT ((length = width) AND (length IS NULL) AND
(width IS NULL)) should likely work.
I'd like to do this in the Lookup class. We can't do this directly in
as_sql() as we don't have enough context there. Maybe a new method
`get_extra_restriction(self, is_negated)` could work. The method returns
an expression (a Lookup instance or WhereNode instance) that will be ANDed
to the lookup's main condition. I'll try to find the time to write a small
proof of concept.
--
Ticket URL: <https://code.djangoproject.com/ticket/23797#comment:6>
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