# rpc error: code = AlreadyExists desc = user with email 'a@b.com' already exists

- **ID:** `go/grpc-already-exists-duplicate-resource`
- **Domain:** go
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The server rejected a create because a unique constraint (email, ID, etc.) was violated. Often caused by retries without idempotency keys.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.0+ | active | — | — |

## Workarounds

1. **** (90% success)
   ```
   md := metadata.Pairs("idempotency-key", uuid.NewString())
ctx := metadata.NewOutgoingContext(ctx, md)
_, err := client.CreateUser(ctx, req)
   ```
2. **** (85% success)
   ```
   if status.Code(err) == codes.AlreadyExists {
  existing, _ := client.GetUser(ctx, &pb.GetUserReq{Email: req.Email})
  return existing, nil
}
   ```

## Dead Ends

- **** — The existing resource may differ from the intended one; silently accepting hides data bugs (70% fail)
- **** — Creates duplicate logical entities and violates business rules (85% fail)