sqlalchemy -如何从联合查询中选择计数

from sqlalchemy import create_engine, func
from sqlalchemy.orm import sessionmaker

# 创建数据库引擎
engine = create_engine('数据库连接字符串')

# 创建会话工厂
Session = sessionmaker(bind=engine)
session = Session()

# 定义模型类
class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    # 其他字段...

class Order(Base):
    __tablename__ = 'orders'
    id = Column(Integer, primary_key=True)
    user_id = Column(Integer, ForeignKey('users.id'))
    # 其他字段...

# 联合查询并选择计数
count = session.query(func.count(Order.id)).join(User).filter(User.name == 'John').scalar()

print(f"John的订单数量为: {count}")