#25789: Inefficient Queries Generated due to not using WHERE EXISTS
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Reporter: cancan101 | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by akaariai):
Yes, this is possible, and something Django's ORM should do.
Unfortunately this is hard to implement correctly. The big problem is
aggregation, when doing .filter().annotate(), where both operations target
the same relation, the aggregation must use results of the join generated
by the filter. But if the filter doesn't generate a join, then we have a
problem.
It would be Djangoic if the exists query would be generated automatically.
For the above mentioned reason this is hard. Maybe it would be easier if
we had something like .filter(models.Exists(somerel__col=val)), where the
Exists() class would inform Django that an exists subquery should be
generated.
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Ticket URL: <https://code.djangoproject.com/ticket/25789#comment:2>
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