public abstract class MyController: Controller
{
    public MyDbContext db { get; set; }
}

protected void Application_Start()
    {
[..]
        var builder = new ContainerBuilder();

        builder.RegisterControllers(typeof(MvcApplication).Assembly).PropertiesAutowired();

        var container = builder.Build();
        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

        builder.RegisterType<MyDbContext>().InstancePerHttpRequest();


    }