#21760: prefetch_related uses an inefficient query to get the related fk data
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Reporter: valtron2000@… | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.6
(models, ORM) | Resolution:
Severity: Release blocker | Triage Stage: Accepted
Keywords: prefetch_related | Needs documentation: 0
ForeignKey | Patch needs improvement: 0
Has patch: 1 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
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Comment (by loic84):
We discussed this issue with @akaariai on IRC.
Like we did for #21410, we'll take a practical approach for fixing the
regression from Django 1.6 to master and go for the proposed fix. It's
worth noting that the inefficient query will still be present for
multicolumn relations, but these are not documented and one needs to use
private APIs to make them, so that doesn't qualify as a regression.
The implementation of
`ReverseSingleRelatedObjectDescriptor.get_prefetch_queryset()` really
ought to be cleaned up at some point, especially when we land the patch
for composite fields but it'll require a fair amount of refactoring so it
only qualifies for master.
@valtron2000, would you mind updating the patch?
- The "FIXME" comment would have to be updated to explain this the new
case with a reference to this ticket.
- The current test is pretty fragile, could you rather check in QS.query
if there is a join?
Feel free to open a PR on github.
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Ticket URL: <https://code.djangoproject.com/ticket/21760#comment:11>
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