.NET and C# interview questions

Thread-safe dictionary operations without a coarse lock for every access.

It treats an in-memory sequence as IQueryable so expression trees can be composed.

MapControllers enables attribute-routed controller endpoints.

I return FileStreamResult or Results.File with the right content type and content-disposition.

They run set-based updates and deletes without loading entities into memory.

They eager-load related data in one query.

I add an IsDeleted flag and a global query filter.

Clients present a TLS client cert that middleware maps to a user.

I store the key ring in a shared location and let new keys activate while old ones decrypt existing cookies.

It creates stubs and verifies interactions on interfaces.

I inject an abstraction for UtcNow instead of DateTime.UtcNow directly.

Factory creates short-lived contexts for parallel or background work.

BeginScope attaches properties to subsequent log calls in that block.

The configuration stack layers providers

Formatters choose JSON or XML based on Accept headers when configured.

You need GetAwaiter returning something with IsCompleted, OnCompleted, and GetResult.

ref struct types like Span can only live on the stack so they can safely point at stack memory.

I never block on .Result or .Wait in ASP.NET request threads.

Expand then contract: add nullable columns, dual-write, backfill, switch reads, drop later.

SaveChanges and command interceptors add auditing, multi-tenant filters, or soft-delete stamps.