sqlalchemy has no base

main.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()
from models import User


def create_app(config=None):
    app = Flask("testing")
    app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite://"
    db.init_app(app)
    with app.app_context():
        db.create_all()

    @app.route('/')
    def default():

        return "hello to " + ", ".join(User.query.all())
    return app

models_model.py

# this file is in the models/ folder
from sqlalchemy import Column, String
from app import db


class User(db.Base):
    __tablename__ = "user"
    name = Column(String, nullable=False)

    def __repr__(self):
        return f"<User name={self.name}>"

def init_data(db):
    db.session.add_all([
        User("frank"),
        User("jim"),
        User("paul")
    ])
    db.session.commit()