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.NET Core / Web API70 min total · 19 parts

Building REST APIs with ASP.NET Core: Routing, Middleware, and Dependency Injection

Contents — Part 2 of 19: The Minimal Hosting Model and Program.cs
  1. 1.Overview
  2. 2.The Minimal Hosting Model and Program.cs
  3. 3.The Middleware Pipeline
  4. 4.Routing: Attributes Map a URL to a Method
  5. 5.Controllers, [ApiController], and ControllerBase
  6. 6.Model Binding: Where Parameters Come From
  7. 7.Model Validation with Data Annotations
  8. 8.Action Results and Status Codes
  9. 9.Dependency Injection and Service Lifetimes
  10. 10.Configuration and the Options Pattern
  11. 11.Entity Framework Core: DbContext Lifetime and Async Queries
  12. 12.Authentication and Authorization Middleware
  13. 13.CORS
  14. 14.Error Handling and ProblemDetails
  15. 15.Filters: Cross-Cutting Logic Around Actions
  16. 16.API Versioning and Documentation
  17. 17.Async/Await Throughout the Pipeline
  18. 18.Testing Web API Controllers
  19. 19.Common Mistakes Worth Remembering
Part 2 of 19 · ~1 min

The Minimal Hosting Model and Program.cs

Modern ASP.NET Core (from .NET 6 onward) uses a single top-level Program.cs file instead of the older split Program/Startup classes — functionally equivalent, just less ceremony:

var builder = WebApplication.CreateBuilder(args);

// Registering services with the DI container happens here, before Build()
builder.Services.AddControllers();
builder.Services.AddScoped<IOrderService, OrderService>();

var app = builder.Build();

// Configuring the middleware pipeline happens here, after Build()
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();

app.Run();

WebApplicationBuilder separates two distinct phases: service registration (builder.Services.Add..., populating the DI container that will construct your controllers and their dependencies) happens before Build(); middleware configuration (app.Use..., app.Map..., building the pipeline a request actually flows through) happens after. Mixing these up — trying to register a service after Build(), for instance — is a compile-time or runtime error depending on exactly what's attempted, because WebApplication (returned by Build()) no longer exposes the same service-registration surface as WebApplicationBuilder.

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Overview
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The Middleware Pipeline