from datetime import datetime
from sqlalchemy import create_engine, Column, Integer, String, DateTime
from sqlalchemy.orm import declarative_base, sessionmaker

Base = declarative_base()

class User(Base):
    __tablename__ = "users"
    id = Column(Integer, primary_key=True)
    username = Column(String(50), unique=True, nullable=False)
    email = Column(String(100), nullable=False)
    created_at = Column(DateTime, default=datetime.utcnow)

engine = create_engine("sqlite:///example.db")
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)

with Session() as session:
    session.add(User(username="charlie", email="charlie@example.com"))
    session.commit()
    for u in session.query(User).filter(User.username == "charlie"):
        print(u.id, u.email)