What are shadow keys / foreign keys?

Short answer: A shadow property is a property not defined in the .NET class but exists in the EF model.

Example code

modelBuilder.Entity<Post>() .HasOne<Blog>() .WithMany() .HasForeignKey("BlogId"); // BlogId is a shadow FK if not defined in class EF tracks it internally but you can't access it in C# code directly.

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.