Historical migrations with index_together crash on Django 5.1+ for partitioned models (TypeError: 'class Meta' got invalid attribute(s): index_together)

[lorthirk]

Disclaimer: Co-Authored with Claude Code

Environment

• django-postgres-extra: 2.0.9 (same code on master)
• Django: 5.2.16 (reproduces on any 5.1+)
• Python: 3.12 · PostgreSQL: 18

Summary

On Django 5.1+, applying/rendering a historical migration that contains index_together
(via migrations.AlterIndexTogether(...) or CreateModel(options={'index_together': ...}))
for a PostgresPartitionedModel crashes:

TypeError: 'class Meta' got invalid attribute(s): index_together
  … psqlextra/backend/migrations/state/model.py:98 render
    return type(*self._pre_render(self.name, bases, attributes))
  … psqlextra/models/partitioned.py:23 __new__
  … django/db/models/base.py:145 add_to_class → Options(meta, app_label)
  … django/db/models/options.py:227 contribute_to_class → raise TypeError

Stock (non-partitioned) models are NOT affected — only partitioned models rendered by psqlextra.

Root cause

Django 5.1 removed index_together from django.db.models.options.DEFAULT_NAMES. Django fixed
its own state rendering to tolerate index_together in historical ModelState
(ticket #34856, commit b44efdfe, backported to 5.1.x as 2ee6ca6d); AlterIndexTogether stays
supported for historical migrations.

But PostgresPartitionedModelState.render() builds Meta straight from self.options:

    meta = type("Meta", (), {"app_label": self.app_label, "apps": apps, **self.options})

so index_together (still in historical state) is passed to Options.contribute_to_class,
which now rejects it. _pre_render() doesn't filter it either. This bypasses Django's #34856
handling. master has identical code.

Steps to reproduce

1. A PostgresPartitionedModel that once used index_together, with the historical migration
   still present (AlterIndexTogether, or index_together in a CreateModel options dict).
2. On Django ≥ 5.1, run manage.py migrate (or the test runner — migrates from scratch).
3. → TypeError: 'class Meta' got invalid attribute(s): index_together

Expected

Historical partitioned-model state containing index_together should render without crashing on
Django 5.1+, consistent with stock Django after #34856 — no forced hand-editing of migrations.

Suggested fix

Mirror Django's #34856 handling in the partitioned state render(): before building the Meta
class, drop options no longer accepted by the current Options (notably index_together) from
self.options — e.g. filter to keys in Options.DEFAULT_NAMES, or explicitly pop
index_together.

Workaround

Hand-edit the historical migrations to use AddIndex with explicit index names; for existing
DBs, reconcile physical index names with a conditional RenameIndex(old_fields=...) / RunSQL
migration that renames only when the old-named index exists (validate against a prod-like DB).