How to configure a one-to-many relationship?

Short answer: Fluent API: modelBuilder.Entity<Blog>() .HasMany(b => b.Posts) .WithOne(p => p.Blog) .HasForeignKey(p => p.BlogId); Data annotations: public class Post { public int BlogId { get; set; } [ForeignKey("BlogId")] public Blog Blog { get; set; } } A foreign key exists in the many-side entity (Post). EF infers this relationship from navigation + FK.

Example code

Fluent API: modelBuilder.Entity<Blog>() .HasMany(b => b.Posts) .WithOne(p => p.Blog) .HasForeignKey(p => p.BlogId); Data annotations: public class Post
{
public int BlogId { get; set; } [ForeignKey("BlogId")] public Blog Blog { get; set; }
} A foreign key exists in the many-side entity (Post). EF infers this relationship from navigation + FK.

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.