Minimal flask-sqlalchemy integration, which allows you to keep models independent of flask

flask_sqlalchemy.py

from typing import TYPE_CHECKING

from sqlalchemy import create_engine 
if TYPE_CHECKING:
    from flask import Flask
    from sqlalchemy.orm import scoped_session


class FlaskSQLAlchemy:

    def __init__(self, app: 'Flask' = None, db: 'scoped_session' = None) -> None:
        self.engine = None
        if app and db:                
            self.init_app(app, db)          
  
    def init_app(self, app: 'Flask', db: 'scoped_session') -> None:
        if not app or not db:
            raise ValueError
        app.extensions['sqlalchemy'] = self
  
        uri = app.config.setdefault('SQLALCHEMY_DATABASE_URI', 'sqlite:///:memory:')
        options = app.config.setdefault('SQLALCHEMY_ENGINE_OPTIONS', {})
    
        self.engine = engine = create_engine(uri, **options)
        db.configure(bind=engine)

        # pylint: disable=unused-variable
        @app.teardown_appcontext
        def shutdown_session(response_or_exc):
            db.remove()        
            return response_or_exc

models.py

from sqlalchemy.orm import scoped_session
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

session_factory = sessionmaker()
db = scoped_session(session_factory)
Model = declarative_base()
metadata = Model.metadata

from .mymodel import MyModel

mymodel.py

from sqlalchemy import Column, Integer, Text
from .models import Model


class MyModel(Model):
    __tablename__ = 'my_model'
    
    id = Column(Integer, primary_key=True)
    name = Column(Text, nullable=False)

test_misc.py

import pytest
from .models import db, metadata
from .mymodel import MyModel


@pytest.fixture
def with_flask():
    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
    sa = FlaskSQLAlchemy()
    sa.init_app(app, db)
    with app.app_context() as ctx:
        metadata.create_all(sa.engine)
        yield

        
@pytest.fixture
def without_flask():
    engine = create_engine('sqlite:///:memory:')
    db.configure(bind=engine)
    try:
        metadata.create_all(engine)
        yield
    finally:
        db.remove()

        
@pytest.mark.usefixtures('with_flask')
def test_simple():
    item = MyModel(name='hello')
    db.add(item)
    db.commit()
    item = db.query(MyModel).filter_by(name='hello').first()
    assert item.name == 'hello'

    
@pytest.mark.usefixtures('without_flask')
def test_simple2():
    item = MyModel(name='world')
    db.add(item)
    db.commit()
    item = db.query(MyModel).filter_by(name='world').first()
    assert item.name == 'world'