#36857: Add totally_ordered property to QuerySet to check for deterministic
ordering
-------------------------------------+-------------------------------------
Reporter: VIZZARD-X | Type: New
| feature
Status: new | Component: Database
| layer (models, ORM)
Version: 6.0 | Severity: Normal
Keywords: ordering | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Currently, `QuerySet.ordered` returns `True` if any ordering is applied,
but this does not guarantee deterministic results. For example, ordering
by a non-unique field (like `pub_date`) is considered "ordered", but the
relative order of records with the same date is undefined and database-
dependent.
This lack of determinism causes issues in pagination and serialization
(specifically for natural keys), where a stable sort order is required to
ensure consistency.
I propose adding a property (tentatively `totally_ordered`) to `QuerySet`
that checks if the applied ordering is sufficient to guarantee a stable
sort. This would verify if the order clauses include a unique field (like
the primary key) or a set of fields covered by a unique constraint.
Note: Similar logic already exists in
`django.contrib.admin.views.main.ChangeList.get_ordering`. The plan is to
extract that logic, make it public/reusable on `QuerySet`, and document
it.
Context: This feature was identified as a requirement for fixing #36750
(deterministic M2M serialization).
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Ticket URL: <https://code.djangoproject.com/ticket/36857>
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