#25467: Excluding an object with no ID excludes everything.
-------------------------------------+-------------------------------------
Reporter: skorokithakis | Owner:
| HuffAndPuff
Type: Bug | Status: assigned
Component: Database layer | Version: 1.8
(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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Comment (by carljm):
Some more musings on this:
Our strongest existing precedent for the meaning of `None` in an ORM
comparison is that `__exact=None` is equivalent to `__isnull=True`, or SQL
`IS NULL`.
If we accept that as a consistent semantic, it would imply that we should
fix `__in=[val, None]` generally (not just for related fields) to remove
the `None` from the `in` list and add an `OR IS NULL` clause alongside it.
This seems better than the current behavior to me, but perhaps low
priority.
It would also imply that `.exclude(related_field=unsaved_instance)` would
exclude records where the `related_field` FK is `NULL`. This is subtly
different from the OPs requested behavior, which is that such an `exclude`
would never exclude anything. I find the latter behavior (to consider
`unsaved_instance` to match nothing, rather than matching NULL) more
intuitive. Which means we either a) use different semantics for instance-
with-None-pk in comparisons than we use for `None` in comparisons
otherwise, b) accept a less-intuitive behavior for instance-with-None-pk
for consistency with use of `None` elsewhere, or c) declare that the
choice between (a) and (b) is too ambiguous (that I was wrong earlier when
I said "there's no ambiguity"), and therefore we should just raise an
exception after all.
I think I would put these in preference order (a) (c) (b), but could live
with any of them; and complexity-of-implementation could easily sway me to
prefer (c) over (a).
--
Ticket URL: <https://code.djangoproject.com/ticket/25467#comment:9>
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