Domain Driven Design Aggregate Root Example in Python

from __future__ import annotations
from dataclasses import dataclass
from typing import List, Optional
from uuid import uuid4


class Money:
    def __init__(self, amount: float, currency: str = "USD"):
        self.amount = amount
        self.currency = currency

    def __add__(self, other: Money) -> Money:
        if self.currency != other.currency:
            raise ValueError("Currency mismatch")
        return Money(self.amount + other.amount, self.currency)

    def __repr__(self) -> str:
        return f"${self.amount:.2f} {self.currency}"


@dataclass
class OrderItem:
    product_id: str
    quantity: int
    price: Money

    def total(self) -> Money:
        return Money(self.price.amount * self.quantity, self.price.currency)


class Order:
    def __init__(self, customer_id: str):
        self.order_id = str(uuid4())[:8]
        self.customer_id = customer_id
        self.items: List[OrderItem] = []
        self.status = "pending"

    def add_item(self, product_id: str, quantity: int, price: Money) -> None:
        if self.status != "pending":
            raise ValueError("Order is no longer editable")
        self.items.append(OrderItem(product_id, quantity, price))

    def calculate_total(self) -> Money:
        total = Money(0.0)
        for item in self.items:
            total = total + item.total()
        return total

    def submit(self) -> None:
        if not self.items:
            raise ValueError("Cannot submit empty order")
        if self.status != "pending":
            raise ValueError("Order already submitted")
        self.status = "submitted"


def main() -> None:
    order = Order(customer_id="CUST-123")
    order.add_item("PROD-SHOES", 2, Money(59.99))
    order.add_item("PROD-SOCKS", 3, Money(4.50))
    print(f"Order {order.order_id} total: {order.calculate_total()}")
    order.submit()
    print(f"Order status: {order.status}")
    try:
        order.add_item("PROD-HAT", 1, Money(19.99))
    except ValueError as e:
        print(f"Error: {e}")


if __name__ == "__main__":
    main()