在SQLAlchemy中使用适当的文件结构，以及如何将数据添加到数据库

from sqlalchemy import Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    username = Column(String(50), unique=True)
    password = Column(String(50))

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine('sqlite:///database.db')
Session = sessionmaker(bind=engine)
session = Session()

from models import User
from database import session

# 创建一个新用户并添加到数据库
new_user = User(username='john', password='password123')
session.add(new_user)
session.commit()

# 查询所有用户
users = session.query(User).all()
for user in users:
    print(user.username)