Adding Startup.cs back to .NET 6 Project

When NET 6 was released, the first big change was the lack of Startup.cs. This is very nice and all. But sometimes we just want it back, and here is how.

First, create a new file called Startup.cs at the root of your project with the following content - don't forget the namespace.

public class Startup
{
    readonly IConfiguration configuration;

    public Startup(IConfiguration configuration)
    {
        this.configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}

Then at Program.cs change to the following.

//add necessary usings

var builder = WebApplication.CreateBuilder(args);

//create new instance of Startup
var startup = new Startup(builder.Configuration);

//configure all services
startup.ConfigureServices(builder.Services);

var app = builder.Build();

//configure the pipeline
startup.Configure(app, builder.Environment);

//run
app.Run();

The simplest solution is the better!

That is it. Enjoy.

Comments

[Pierre Bouillon]

The Program.cs seems to be missed by many developers!

I happened to look at the preview of .NET 7 and you should be pretty happy since it introduce back the Program.cs for those who want it. All you will need to do is appending --use-program-main to your command line:

This will also be supported directly by Visual Studio (I just find odd that a checkbox is for not enabling something):

Hope it might save @stphnwlsh the extension method and give an alternative to @kaylumah!

[Ricardo]

Super cool

[Stephen Walsh]

Hey that's pretty cool, but honestly I don't mind the new setup. I just don't want everything in the one file. It's maybe cool for small projects or little things but when you're configuring logging, telemetry, swagger etc that Program.cs blows out quickly.

I can easily create extension methods on the WebApplicationBuilder and WebApplication in say a ProgramExtensions.cs file and I find it helps with that separation, just like Startup.cs did.

Also not a huge fan of the minimal api setup, but if when implementing those, I'd use extension methods to separate out pseudo controllers too

[Pierre Bouillon]

I have to admit that you are right, the Program.cs does look like a good idea but the fact that it is blowing up when configuring a bigger application might show that it may not be the best way to reduce the boilerplate

As for minimal API it seems that a lot of people are doing the same. Still in .NET 7, they introduces RouteGroups to create such pseudo-controllers and keep it a little bit more coherent

However, I think that it may not be ideal if you are defining endpoints in a single pseudo-controller and they all have specific configuration as for their routes / authorization / metadata / etc.

[Karanveer Singh]

I think people will still use the Startup and Program classes for a while because most of the books on ASP.NET still have them as examples.
Thanks for making this reference available!

[Max Hamulyák]

I am still not sure what I think of the change they made to the template. Sure it's nice to write less code, and I supose its more beginner friendly. But in my opinion its also less verbose.

[Stephen Walsh]

I've just build into the new format with extension methods. Have to fix the naming but works for me.

public static WebApplicationBuilder ConfigureBuilder(this WebApplicationBuilder builder)