取货数量的任意逻辑使用条件

def update_stock(product_id, quantity):
    product = Product.query.get(product_id)
    if product.stock >= quantity:
        product.stock -= quantity
        product.version += 1  # 乐观锁版本号
        db.session.commit()
    else:
        raise ValueError("库存不足")

class PickupStrategy:
    def calculate_quantity(self, order):
        pass

class DefaultStrategy(PickupStrategy):
    def calculate_quantity(self, order):
        return min(order.quantity, self.get_available_stock(order.product_id))

class PromotionStrategy(PickupStrategy):
    def calculate_quantity(self, order):
        # 特殊促销逻辑
        return ...

def get_pickup_strategy(order):
    if order.is_promotion:
        return PromotionStrategy()
    return DefaultStrategy()

# 使用策略
strategy = get_pickup_strategy(order)
quantity = strategy.calculate_quantity(order)