How to Build a Daily Card Feature Without a Database Using Hash Functions

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A developer has shared a stateless approach to implementing a 'card of the day' feature that avoids the need for per-user database writes. The method uses a deterministic hash function — such as FNV-1a or xxhash — seeded with a combination of user ID, date, and deck version to always return the same card for a given user on a given day. Timezone handling remains a practical challenge, and the author settled on accepting client-reported dates while validating them within a ±1-day window of UTC. Including a deck version in the seed prevents retroactive card shifts when new cards are added to the deck. The technique is already in use on a live app called Oraclely and is best suited for ephemeral draws where storing draw history is not required.

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