[vishalkaay]

Every SQLAlchemy list view fails with AttributeError: 'SQLAlchemy' object has no attribute 'query' when Flask-SQLAlchemy-Lite is used with SQLAlchemy 2.1 and greenlet is not installed (#2994).

Cause. SQLAlchemy 2.1 no longer installs greenlet by default. flask_sqlalchemy_lite imports sqlalchemy.ext.asyncio, which raises ImportError without it. That import fails only the first time in a process; a second attempt succeeds:

>>> from flask_sqlalchemy_lite import SQLAlchemy
ImportError: The SQLAlchemy asyncio module requires that the Python 'greenlet' library is installed. ...
>>> from flask_sqlalchemy_lite import SQLAlchemy
>>> SQLAlchemy
<class 'flask_sqlalchemy_lite._extension.SQLAlchemy'>

flask_admin/contrib/sqla/_types.py catches the ImportError and sets T_SQLALCHEMY_LITE = None. So when flask_admin is imported before the application imports flask_sqlalchemy_lite, Flask-Admin absorbs the one failure, the application's import works, and _is_db_extension(db) is false for the application's db object. get_query() then calls .query on the extension instead of its session. SQLAlchemy 2.0 is unaffected because it depends on greenlet.

Change. _is_db_extension() now falls back to the flask_sqlalchemy_lite module in sys.modules when Flask-Admin's own import failed. An application can only hold a Flask-SQLAlchemy-Lite db object if that module is loaded, so the object is recognised whichever import ran first. Nothing changes when the import in _types succeeds, or when the package cannot be imported at all (e.g. installed next to SQLAlchemy 1.4).

The first version of this PR re-raised the import error instead. That broke py311-min, where Flask-SQLAlchemy-Lite is installed alongside SQLAlchemy 1.4 and can never import, so I replaced it with this approach.

The new test simulates the failed import and checks that a view created with a Flask-SQLAlchemy-Lite db object still serves its list view. It fails on master. I also checked the real case by hand: SQLAlchemy 2.1.1 without greenlet now returns 200 for the list view.

fixes #2994

[ElLorans]

Isn't this a bug in flask-sqlalchemy-lite or even asyncio/(greenlet more than in flask-admin?
Why do we need additional test case? Upgrading the lockfile is sufficient

[ElLorans]

flask-sqla-lite even declares "sqlalchemy[asyncio]>=2.0.31", as a dependency, so greenlet should be installed when flask-sqlalite is present

[ElLorans]

even uv tree --script a.py marks greenlet as required dependency of flask-sqla-lite

Resolved 14 packages in 12ms
sqlalchemy v2.1.8
└── typing-extensions v4.16.0
flask-sqlalchemy-lite v0.2.1
├── flask[async] v3.1.3
│   ├── blinker v1.9.0
│   ├── click v8.5.1
│   ├── itsdangerous v2.2.0
│   ├── jinja2 v3.1.6
│   │   └── markupsafe v3.0.4
│   ├── markupsafe v3.0.4
│   ├── werkzeug v3.1.9
│   │   └── markupsafe v3.0.4
│   └── asgiref v3.13.0 (extra: async)
└── sqlalchemy[asyncio] v2.1.8
    ├── typing-extensions v4.16.0
    └── greenlet v3.5.6 (extra: asyncio)
flask-admin v2.2.1
├── flask v3.1.3
│   ├── blinker v1.9.0
│   ├── click v8.5.1
│   ├── itsdangerous v2.2.0
│   ├── jinja2 v3.1.6 (*)
│   ├── markupsafe v3.0.4
│   └── werkzeug v3.1.9 (*)
├── jinja2 v3.1.6 (*)
├── markupsafe v3.0.4
├── werkzeug v3.1.9 (*)
└── wtforms v3.3.2
    └── markupsafe v3.0.4