Is there a way to use Autofac Service Registration With Microsoft DI

Question

I have some legacy projects that use Autofac for their DI container and they have all of their registration nicely organized into Modules. I have a new .net 8 API project and some flows need to reference these legacy projects. Rather than re-register all of my legacy dependencies, is there a way to use the already created Modules and register those with my IServiceCollection? Ive been looking over Autofac's documentation and the only thing I see is using Microsoft's registration with Autofac, where Autofac becomes the main container. I would like to keep Microsoft as my main container, but just use Autofac for registering old services. The only thing I saw that looked like it might do what I want was with the Autofac.Extensions.DependencyInjection package where I tried:

services.AddAutofac(builder => builder 
{
    builder.AddModule(new LegacyModule);
});

but it looks like AddAutofac is deprecated and didn't work how I expected anyway.

Answer 1

Following code works to register autofac module to default Webapplicationbuilder. Assume you have this module:

    public class Student
    {
        public string Name { get; set; } = "Tom";
    }

    public class MyAutofacModule : Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            builder.RegisterType<Student>();
        }
    }

Then you could add to webapi like

builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());

builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    containerBuilder.RegisterModule(new MyAutofacModule());
});

Package Autofac.Extensions.DependencyInjection

-------Below is startup pattern-----

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseServiceProviderFactory(new AutofacServiceProviderFactory())
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

Startup.cs

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

    // ConfigureContainer is where you can register things directly with Autofac.
    public void ConfigureContainer(ContainerBuilder builder)
    {
        // Register your Autofac modules or registrations here
        builder.RegisterModule(new MyAutofacModule());
    }