How to implement the Database per service pattern in Python

import json
from dataclasses import dataclass, asdict
from typing import Dict, List


@dataclass
class User:
    id: int
    name: str
    email: str


@dataclass
class Order:
    id: int
    user_id: int
    product: str
    amount: float


class UserServiceDB:
    """Simulates a separate database for the User service."""
    def __init__(self) -> None:
        self._users: Dict[int, User] = {}

    def create_user(self, user: User) -> User:
        self._users[user.id] = user
        return user

    def get_user(self, user_id: int) -> User | None:
        return self._users.get(user_id)


class OrderServiceDB:
    """Simulates a separate database for the Order service."""
    def __init__(self) -> None:
        self._orders: Dict[int, Order] = {}

    def create_order(self, order: Order) -> Order:
        self._orders[order.id] = order
        return order

    def get_orders_for_user(self, user_id: int) -> List[Order]:
        return [o for o in self._orders.values() if o.user_id == user_id]


if __name__ == "__main__":
    user_db = UserServiceDB()
    order_db = OrderServiceDB()

    user_db.create_user(User(id=1, name="Alice", email="alice@example.com"))
    order_db.create_order(Order(id=101, user_id=1, product="Laptop", amount=1200.00))
    order_db.create_order(Order(id=102, user_id=1, product="Mouse", amount=25.50))

    user = user_db.get_user(1)
    orders = order_db.get_orders_for_user(1)

    print(json.dumps({
        "user": asdict(user) if user else None,
        "orders": [asdict(o) for o in orders]
    }, indent=2))