migrating-autofac-to-dotnet-di

name	migrating-autofac-to-dotnet-di
description	Removes Autofac entirely and migrates to ASP.NET Core built-in DI by mapping container registrations, lifetimes, and module patterns. Use when upgrading .NET projects that reference Autofac packages, when converting ContainerBuilder registrations, or when replacing Autofac modules with IServiceCollection extensions. Triggers for "replace Autofac", "remove Autofac", "migrate to built-in DI", "convert dependency injection", Autofac.Extensions.DependencyInjection, RegisterType, InstancePerLifetimeScope, and ContainerBuilder references in C# or VB.NET projects.
metadata	{"traits":".NET|CSharp|VisualBasic|DotNetCore","discovery":"lazy"}

Autofac to ASP.NET Core DI Migration

Overview

Converts Autofac DI registrations to ASP.NET Core's built-in IServiceCollection pattern. The built-in container covers most registration scenarios; assembly scanning requires the Scrutor NuGet package.

Related skill: If the goal is to keep Autofac but modernize its integration with ASP.NET Core, use integrating-autofac-with-dotnet instead.

Verification

Before starting, confirm the project actually uses Autofac. Search for Autofac NuGet references and ContainerBuilder usage. If none found, inform the user there is nothing to migrate.

Workflow

Migration Progress:
- [ ] Step 1: Locate Autofac registrations
- [ ] Step 2: Document all registrations
- [ ] Step 3: Remove Autofac code
- [ ] Step 4: Remove Autofac packages
- [ ] Step 5: Create registration helper
- [ ] Step 6: Wire into Program.cs
- [ ] Step 7: Build and verify

Step 1: Locate Autofac registrations

Find ContainerBuilder setup code (check global.asax.cs, Startup.cs, or Autofac module classes).

Step 2: Document all registrations

Record each service registration and its lifetime scope before removing anything.

Step 3: Remove Autofac code

Delete the container builder code that will be replaced.

Step 4: Remove Autofac packages

Remove Autofac, Autofac.Extensions.DependencyInjection, and any other Autofac-related NuGet packages.

Step 5: Create registration helper

Add a static helper method that registers all services on IServiceCollection, using the lifetime mapping table below.

Step 6: Wire into Program.cs

Call the helper method from Program.cs, passing builder.Services.

Step 7: Build and verify

Build the project, fix any remaining Autofac references, confirm no regressions.

Lifetime Mapping

Autofac	ASP.NET Core DI	Notes
InstancePerDependency()	AddTransient<T>()	Default Autofac lifetime
InstancePerLifetimeScope()	AddScoped<T>()	One per request in web apps
InstancePerRequest()	AddScoped<T>()	Web-specific alias for scoped
SingleInstance()	AddSingleton<T>()
RegisterInstance(obj)	AddSingleton(obj)
RegisterAssemblyTypes(...)	services.Scan(...)	Requires Scrutor package

Common Patterns

Interface registration:

// Autofac
builder.RegisterType<MyService>().As<IMyService>().InstancePerLifetimeScope();
// Built-in DI
services.AddScoped<IMyService, MyService>();

Registration helper pattern — isolates DI setup for testability and keeps Program.cs clean:

// In Program.cs
var builder = WebApplication.CreateBuilder(args);
RegisterServices(builder.Services, builder.Configuration);
var app = builder.Build();

static void RegisterServices(IServiceCollection services, IConfiguration configuration)
{
    services.AddScoped<IMyService, MyService>();
    services.AddSingleton<IMyOtherService, MyOtherService>();
}

Troubleshooting

• Missing registrations at runtime — Compare the documented Autofac registrations against the new helper method. Autofac's default lifetime is InstancePerDependency (transient), so unspecified lifetimes should map to AddTransient.
• Assembly scanning — If the project used RegisterAssemblyTypes, add the Scrutor NuGet package (dotnet add package Scrutor) and use services.Scan(...) to replicate the behavior.

Success Criteria

• All Autofac packages removed from project files
• No ContainerBuilder or Autofac namespace references remain
• All service lifetimes correctly mapped per the table above
• Project builds without errors