They gave you a choice between using an AI tool or doing it the traditional way.
Start by clarifying functional and non-functional requirements, then define core entities and their relationships using OOP principles. Walk through the design iteratively, explaining trade-offs and how you would handle scalability, concurrency, and extensibility.
Pro tip: Demonstrate maturity by discussing how your design would evolve over time—e.g., from a monolithic OOP model to a distributed system—and highlight where you'd apply design patterns like Strategy or Observer to keep components decoupled.
Ask questions to understand scope: user roles (customer, restaurant, driver), key features (order placement, tracking, payment), and non-functional needs (scalability, latency, consistency).
Define main classes like User, Restaurant, Menu, Order, Delivery, and Payment. Establish their attributes, methods, and associations (e.g., one-to-many, inheritance).
Use encapsulation, inheritance, and polymorphism to model behavior. Introduce patterns like Factory for order creation, Strategy for payment methods, and Observer for order status updates.
Discuss how to handle high traffic, data consistency, and real-time updates. Mention techniques like caching, message queues, and database sharding.
Explain choices made (e.g., SQL vs NoSQL, synchronous vs asynchronous) and how the design can evolve with new features like ratings or promotions.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
This was the follow-up and it's where things got more interesting.
Clarify requirements first: define 'completed payment' (e.g., captured, settled) and the cutoff semantics (inclusive/exclusive, timezone). Then propose a robust system design that combines a scheduled batch job with real-time monitoring, ensuring idempotency and handling edge cases like late payments or failures.
Pro tip: Mention the importance of idempotency and reconciliation: even if a payment appears complete, you should verify with the payment provider to avoid false positives. Also, consider using a database transaction with row-level locking to prevent race conditions when updating order statuses.
Ask questions to understand what 'completed payment' means (e.g., authorized, captured, settled) and the exact cutoff time semantics (inclusive, timezone). Confirm whether the check is a one-time batch or continuous.
Outline the necessary tables (orders, payments) and the query to find orders placed before cutoff with incomplete payments. Consider indexes on order timestamp and payment status for efficiency.
Decide between a scheduled batch job (e.g., cron) and a real-time stream processing approach. Discuss trade-offs: batch is simpler but may have latency; real-time is complex but immediate.
Address scenarios like payment provider downtime, network failures, and late-arriving payments. Implement retries with exponential backoff, idempotent operations, and dead-letter queues for persistent failures.
Use transactions and locking to avoid race conditions. Set up alerts for orders that remain unpaid after cutoff, and provide a reconciliation report for manual intervention.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.