Root cause: Flask-SQLAlchemy 2.x's SignallingSession.__init__ explicitly
passed `bind=<default engine>` into the SQLAlchemy Session constructor.
Flask-SQLAlchemy 3.x dropped that - it resolves the engine per-call via
Session.get_bind() (consulting the app's registered engines) instead of
fixing one at session-construction time, to support its reworked
multi-engine/multi-bind model. db.session.bind is therefore always None
under FSA 3.x; it was never a documented API, just an implementation
detail of FSA 2.x's Session subclass.
Confirmed locally: `db.session.bind` prints None while
`db.session.get_bind()` correctly resolves the live Engine, against
this branch's real flask-sqlalchemy==3.1.1/sqlalchemy==2.0.51 install.
Fixes the "AttributeError: 'NoneType' object has no attribute 'dialect'"
failures in dashboards/soft_delete_tests.py's partial-index dialect
detection, and pre-emptively fixes the same pattern in
versioning/id_reuse_tests.py (skipped under postgres/current in the CI
run that surfaced this, so not in the failure log there, but broken by
the same mechanism whenever it does run).
Verified locally against both sqlite and a real postgres:17-alpine
container: dashboards/soft_delete_tests.py and
versioning/id_reuse_tests.py pass clean on both backends after this fix.
Claude Code