#32811: Annotate removes Meta.ordering
-------------------------------------+-------------------------------------
Reporter: pirelle | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 3.2
(models, ORM) |
Severity: Release blocker | Resolution: invalid
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 Peter Law):
Request that this be reconsidered.
My use-case was similar to the one mentioned here, however I was loading
full models (with a similar count annotation) and not any form of
`.values()`. Given the history it seems likely that that was never the
intention.
I can see that this was previously deprecated and may now be expected,
however it does not appear to be documented anywhere and is very
surprising.
Here's where I've (since) checked for docs relating to this:
- https://docs.djangoproject.com/en/3.2/ref/models/options/#ordering
- https://docs.djangoproject.com/en/3.2/topics/db/aggregation/
- https://docs.djangoproject.com/en/3.2/ref/models/expressions/#aggregate-
expressions
What I've seen of the reasoning for the deprecation appears to be related
specifically to `.values()` queries, and then really to cases where that
is used to create a grouping ''of the main queried table'' (where the user
is probably aware that that's what they're doing). However the behaviour
change impacts ''all'' querysets (including those which return full
models) and the behaviour here is ''not'' intending to create a grouping
of things on the main table, but rather of a related table for the
purposes of counting (where the user is unlikely to be aware that a group-
by is the result).
Perhaps the core issue here is that the ORM doesn't have an explicit
"group by" mechanism and so is having to infer this by pattern matching
the structure of the `QuerySet`, leading to the issues like the original
one where default ordering is applied in ways that produce potentially
unexpected results.
At the very least I think this (current behaviour) needs to be clearly
documented as a part of both the `Meta.ordering` and aggregation docs,
however to be honest I would prefer the previous behaviour. It feels very
surprising that Django will silently drop part of its model configuration
in some cases!
At least if this were documented people could see what those cases were,
however at the moment the only way to know is when you're bitten by the
issue described here.
Aside: the original ticket (https://code.djangoproject.com/ticket/10574)
appears to suggest that part of the motivation is that in queries such as
`Model.objects.values('data')` applying the default ordering is redundant,
which I'd strongly argue against -- having values-only results ordered by
something (even a field not loaded) seems entirely useful to me.
--
Ticket URL: <https://code.djangoproject.com/ticket/32811#comment:2>
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