#34552: Delaying get_from_clause call as much as possible.
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Reporter: Matthew Schinckel | Owner: Matthew
| Schinckel
Type: New feature | Status: assigned
Component: Database layer | Version: 4.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Simon Charette):
If you need these changes it's likely [https://github.com/schinckel
/django-shared-
property/blob/65b4d5664e503c2b53bbd68f99561e0ea2e3f734/src/django_shared_property/expressions.py#L75
because you are performing expression resolving] during the compilation
phase which is known to cause subtle issues with regards to join reuse and
compilation in general e.g. what if your newly referenced expressions
trigger aggregation or filter against window functions, now you have an
improper `order_by`
It feels like this feature should be implementable by using
`QuerySet.alias` if the latter was implemented in a way that deferred any
form of joining until the alias is first referenced. Am I right in the
assessment that you implemented your expression resolving in `as_sql`
because you wanted to avoid unnecessary JOINs and that if `QuerySet.alias`
allowed you to stash `ordering=models.F('ord__a') / models.F('ord__b')`
without joining into `ord__` until `ordering` is referenced then you could
implement the same feature by simply having `shared_property` augment the
managers querysets with the alias you defined?
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Ticket URL: <https://code.djangoproject.com/ticket/34552#comment:5>
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