How would you handle two requests trying to create the same unique value through EF Core?

Handle unique constraint races in EF Core APIs

Explains why application-level duplicate checks are not enough and how EF Core APIs map database constraints to friendly errors.

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I would keep the database unique constraint as the final authority. The API can check first to return a nicer message, but two requests can pass that check concurrently. When SaveChanges hits the unique constraint, EF Core raises a database update exception. I would catch the specific constraint violation, map it to a clear conflict or validation response, and avoid returning a generic 500.

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Unique constraints, race conditions, DbUpdateException, tenant-scoped uniqueness, validation, and API error mapping.

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Duplicate checks are a classic source of race conditions. EF Core code often looks correct until two requests hit the same path at the same time.
I would keep the database unique constraint as the final authority. The API can check first to return a nicer message, but two requests can pass that check concurrently. When SaveChanges hits the unique constraint, EF Core raises a database update exception. I would catch the specific constraint violation, map it to a clear conflict or validation response, and avoid returning a generic 500.
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I would model the exact uniqueness rule in the constraint. For example, a slug may be unique per tenant, not globally, and an email may need normalization before comparison. If soft deletes exist, the unique index may need a filtered condition or the product may forbid reuse. The application validation and database constraint need to describe the same rule, otherwise the API will behave inconsistently under load.

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Relying only on a pre-insert query to check uniqueness.
Returning a 500 for a known duplicate-key error.
Forgetting tenant scope or normalization.
Mapping every database update exception as duplicate data.

How would you handle two requests trying to create the same unique value through EF Core?

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