.NET and C# interview questions

Server-side caching of endpoint output with policies for duration and tags.

Boxing wraps a value type in an object on the heap

string is immutable so each change may allocate a new string.

It lets you write asynchronous methods with await.

It flags possible nulls at compile time when nullable context is on.

First throws if the sequence is empty.

It projects each element to a sequence and flattens the results into one sequence.

Kestrel is the cross-platform web server built into ASP.NET Core.

Transient creates a new instance every injection.

It loads entities without change tracking, which is faster for read-only queries.

A migration is a versioned change to the database schema generated from the model.

Resolving services from a static container inside business code hides dependencies.

A fake is a working simplified implementation.

They let you write simple members with => instead of a block.

They return values from patterns cleanly and force exhaustive cases with warnings.

It streams async sequences with await foreach.

It avoids capturing the SynchronizationContext after await.

IQueryable can translate expressions to SQL via a provider.

I use Results.Problem or validation ProblemDetails for consistent error JSON.

It selects the endpoint first, then runs middleware that can see the chosen route.