Design a referral feature's lifecycle and races
WHAT IT TESTS: modeling a stateful flow with idempotency and concurrency safety. OUTLINE: a referral entity with explicit states, a unique constraint on the invited user, and atomic transactions plus idempotency to prevent double credits.
WHAT IT TESTS: whether you can model a lifecycle and defend it against concurrency and abuse. ANSWER OUTLINE: a referral record links referrer and referee with a state machine such as sent, accepted, qualified, credited. Enforce a unique constraint so a referee can be referred once, preventing duplicate claims. Apply credits inside an atomic transaction, guarded by idempotency keys and conditional updates, so concurrent acceptances cannot double-pay. Add fraud checks for self-referral and fake accounts.
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- #referral-system
- #state-machine
- #idempotency
- #concurrency
- #data-modeling
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