第1章：后端架构概述¶

# 单体架构示例
class MonolithicApp:
    def __init__(self):
        self.user_service = UserService()
        self.order_service = OrderService()
        self.payment_service = PaymentService()

    def create_order(self, user_id, product_id):
        # 所有服务在一个应用中
        user = self.user_service.get_user(user_id)
        order = self.order_service.create_order(user, product_id)
        payment = self.payment_service.process_payment(order)
        return order

# 垂直拆分架构示例
# 用户服务
class UserService:
    def get_user(self, user_id):
        pass

# 订单服务
class OrderService:
    def create_order(self, user_id, product_id):
        pass

# 支付服务
class PaymentService:
    def process_payment(self, order_id):
        pass

# 微服务架构示例
from fastapi import FastAPI
import requests

# 用户服务
user_app = FastAPI()

@user_app.get("/users/{user_id}")
async def get_user(user_id: int):  # async def定义异步函数；用await调用
    return {"user_id": user_id, "name": "John"}

# 订单服务
order_app = FastAPI()

@order_app.post("/orders")
async def create_order(user_id: int, product_id: int):
    # 调用用户服务
    user = requests.get(f"http://user-service/users/{user_id}").json()
    # 创建订单
    return {"order_id": 1, "user": user}

# 违反SRP
class UserService:
    def create_user(self, user):
        pass

    def send_email(self, email):
        pass  # 发送邮件不是用户服务的职责

# 符合SRP
class UserService:
    def create_user(self, user):
        pass

class EmailService:
    def send_email(self, email):
        pass

# 违反OCP
class PaymentProcessor:
    def process(self, payment_type):
        if payment_type == "alipay":
            # 支付宝逻辑
            pass
        elif payment_type == "wechat":
            # 微信逻辑
            pass

# 符合OCP
class PaymentProcessor:
    def process(self, payment):
        payment.pay()

class AlipayPayment:
    def pay(self):
        pass

class WechatPayment:
    def pay(self):
        pass

# 违反DRY
def get_user_name(user_id):
    user = db.query("SELECT * FROM users WHERE id = ?", user_id)
    return user.name

def get_user_email(user_id):
    user = db.query("SELECT * FROM users WHERE id = ?", user_id)
    return user.email

# 符合DRY
def get_user(user_id):
    return db.query("SELECT * FROM users WHERE id = ?", user_id)

def get_user_name(user_id):
    return get_user(user_id).name

def get_user_email(user_id):
    return get_user(user_id).email