integrating-autofac-with-dotnet

name	integrating-autofac-with-dotnet
description	Migrates Autofac dependency injection configuration from ASP.NET Framework to ASP.NET Core's hosting model while keeping Autofac as the DI container. Use when upgrading projects that use Autofac, migrating Global.asax.cs or Startup.cs DI setup to Program.cs, or integrating AutofacServiceProviderFactory with the generic host. Triggers for Autofac container registration, UseServiceProviderFactory, ContainerBuilder migration, and DependencyResolver removal.
metadata	{"traits":".NET|CSharp|VisualBasic|DotNetCore","discovery":"lazy"}

Register Autofac with ASP.NET Core

Overview

When migrating from ASP.NET Framework to ASP.NET Core, Autofac integration changes significantly. The old pattern of manually building a container and setting DependencyResolver is replaced by registering Autofac as the host's service provider factory. This ensures Autofac participates in the standard DI lifecycle rather than bypassing it.

Related skill: If the goal is to remove Autofac entirely and replace with built-in DI, use migrating-autofac-to-dotnet-di instead.

Workflow

Migration Progress:
- [ ] Step 1: Verify Autofac usage
- [ ] Step 2: Install required package
- [ ] Step 3: Locate and extract existing registrations
- [ ] Step 4: Register Autofac as service provider factory
- [ ] Step 5: Migrate container registrations
- [ ] Step 6: Remove obsolete integration code
- [ ] Step 7: Validate

Step 1: Verify Autofac usage

• Confirm the project uses Autofac for dependency injection. If not, skip — inform the user there is nothing to do.
• Check if Program.cs already calls UseServiceProviderFactory(new AutofacServiceProviderFactory()). If so, verify the container configuration is correct and skip remaining steps.

Step 2: Install required package

Install Autofac.Extensions.DependencyInjection with a version matching the project's target framework. This package provides the AutofacServiceProviderFactory bridge between Autofac and the .NET hosting model.

Step 3: Locate and extract existing registrations

Search for Autofac registration code that builds a container — typically in Global.asax.cs, Startup.cs, or other top-level initialization classes. Record all ContainerBuilder registrations and module registrations before removing that code.

Why remove first? The old code manually calls builder.Build() and sets a DependencyResolver, which conflicts with the host-managed container lifecycle in ASP.NET Core.

Step 4: Register Autofac as service provider factory

Add to Program.cs:

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

Step 5: Migrate container registrations

Move all extracted registrations into a ConfigureContainer block in Program.cs:

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

Omit any calls to builder.Build() or resolver setup — the host handles container building automatically.

Step 6: Remove obsolete integration code

Delete ASP.NET Framework-specific Autofac wiring such as:

• DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
• GlobalConfiguration.Configuration.DependencyResolver = resolver;
• Manual ContainerBuilder.Build() calls in startup code

Step 7: Validate

• Build the project and fix any compilation errors.
• Verify services resolve correctly at runtime.

Example

Before (Global.asax.cs or Startup.cs):

var builder = new ContainerBuilder();
builder.RegisterType<MyService>().As<IMyService>();
builder.RegisterType<MyRepository>().As<IRepository>();
builder.RegisterModule<MyModule>();
var container = builder.Build();
DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

After (Program.cs):

var builder = WebApplication.CreateBuilder(args);

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

builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    containerBuilder.RegisterType<MyService>().As<IMyService>();
    containerBuilder.RegisterType<MyRepository>().As<IRepository>();
    containerBuilder.RegisterModule<MyModule>();
});

var app = builder.Build();

Success Criteria

• Autofac.Extensions.DependencyInjection package installed
• UseServiceProviderFactory configured in Program.cs
• All registrations and modules migrated to ConfigureContainer block
• Obsolete DependencyResolver and manual Build() calls removed
• Project compiles and services resolve correctly at runtime