How do you register services for DI in ASP.NET Core?

Short answer: Services are registered in the Program.cs or Startup.cs file using the IServiceCollection interface.

Example code

builder.Services.AddTransient<IProductService, ProductService>(); builder.Services.AddScoped<IOrderService, OrderService>(); builder.Services.AddSingleton<ILoggingService, LoggingService>();

Real-world example (ShopNest)

Patterns in ShopNest should solve a real pain (swappable payments, test seams)—not be added for decoration.

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.