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System design patterns

Sharding, load balancing, CAP tradeoffs, and scaling patterns — interview and production ready.

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System design patterns easy

How to mock the domain center in an onion architecture in Python

Define a repository interface and an in-memory mock to test domain services without touching infrastructure.

onion-architecture repository-pattern dependency-injection
Python 
from abc import ABC, abstractmethod
from dataclasses import dataclass
from typing import Dict, List, Optional


@dataclass
class Order:
    id: int
    customer: str
    items: List[str]
    total: float


class OrderRepository(ABC):
    @abstractmethod
    def find_by_id(self, order_id: int) -> Optional[Order]:
     …
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