Optimistic CRUD With ETag

To prevent lost updates in concurrent edits, implement optimistic concurrency using integer versioning and ETag headers. The API issues an ETag per entity, and clients must include it on PUT requests to avoid silently overwriting changes made by others.

Optimistic concurrency control using an ETag tracks entity versions to detect conflicts. The API returns an ETag header representing the current version, which clients send back on updates; mismatched versions trigger a 412 Precondition Failed error to prevent overwrites.

To implement optimistic concurrency in Next.js, maintain a version integer on each entity and return it as an ETag header. Clients send this ETag on PUT requests, and the server rejects updates with a 412 Precondition Failed status if the version is outdated.

Optimistic concurrency with ETag works for Expo apps by applying the same version and ETag header pattern. The client reads the ETag from API responses and includes it in subsequent PUT requests to ensure concurrent edits do not cause data corruption.

A PUT request fails with 412 Precondition Failed when the ETag header sent by the client does not match the current entity version on the server. This rejection mechanism prompts the client to re-fetch the latest data before attempting another update.