How to use First, FirstOrDefault, Single, SingleOrDefault etc.?

Short answer: First(): Returns the first element, throws if none found. FirstOrDefault(): Returns first element or default (null) if none. Single(): Returns the single element, throws if zero or more than one. SingleOrDefault(): Returns the single element or default if none; throws if more than one.

Real-world example (ShopNest)

ShopNest’s order service uses EF Core to save an Order and its line items in one SaveChangesAsync() call inside a transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.