如何检查用户电子邮件是否已保存在数据库中

from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    email = Column(String, unique=True, index=True)

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

def check_email_exists(email):
    session = Session()
    user = session.query(User).filter_by(email=email).first()
    return user is not None

# 使用示例
email_to_check = "example@example.com"
if check_email_exists(email_to_check):
    print("Email already exists.")
else:
    print("Email is available.")