Event ticket check-in
Your task
Design a simple event-ticketing check-in system. People buy tickets online and get a unique code (rendered as a QR). At the venue, staff scan codes to admit guests; each ticket must be valid for exactly one entry, and scanning the same code twice should be rejected. There are a few thousand tickets and a few scanning stations. Cover the data model, how check-in works, and how you ensure a ticket can't be used twice.
It covers
- Idempotency
- Validation