from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///example.sqlite"
class Base(DeclarativeBase):
  pass
db = SQLAlchemy(app, model_class=Base)
class User(db.Model):
    id: Mapped[int] = mapped_column(primary_key=True)
    username: Mapped[str] = mapped_column(unique=True)
with app.app_context():
    db.create_all()
    db.session.add(User(username="example"))
    db.session.commit()
    users = db.session.scalars(db.select(User))