.NET and C# interview questions

I add CORS policy with allowed origins, methods, and headers, then UseCors.

It watches loaded entities for property changes and builds INSERT/UPDATE/DELETE on SaveChanges.

I mark a rowversion or token property and EF includes it in WHERE on update.

Identity hashes with a strong algorithm and salt via PasswordHasher.

It encrypts tokens, cookies, and antiforgery payloads with keys managed by the Data Protection API.

I reuse buffers with ArrayPool, avoid boxing, prefer spans, and cut LINQ in tight loops.

I log message templates with named placeholders so sinks index fields.

I split by bounded context folders or projects with clear interfaces, one deployable host.

gRPC shines for internal service-to-service with protobuf and HTTP/2 streaming.

I add IsDeleted and a global query filter, plus careful unique indexes that include the flag.

For huge loads I use bulk extensions, COPY-like tools, or raw SQL, not SaveChanges per row.

I use built-in rate limiter middleware with fixed or sliding windows per IP or user.

I publish multiple validation keys and phase old ones out after token lifetime.

Sync-over-async, blocking calls, and too few threads show as delayed requests with low CPU.

WebApplicationFactory hosts the app in memory with a test server.

I store processed message ids or use natural idempotency keys before side effects.

For string, == compares values due to operator overload.

Dictionary gives fast key lookup.

They generate C# at compile time from analyzers.

Endpoints report if DB and dependencies are healthy for orchestrators.