具有Autofac的ASP.Net MVC构造函数注入-运行时参数

Question

I am reasonably new to Autofac and have come up against a problem when injecting dependencies that have arguments that are only known at runtime. (the code below is an example of the problem I am trying to describe).

Here is where I setup my container (which gets called in Global.asax)

public class Bootstrapper
{
    public static void Config()
    {
        var builder = new ContainerBuilder();
        builder.RegisterControllers(Assembly.GetExecutingAssembly());

        builder.RegisterType<PersonService>().As<IPersonService>().InstancePerHttpRequest();
        builder.RegisterType<PersonRepository>().As<IPersonRepository>().InstancePerHttpRequest();

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

Here are the types.

public class PersonService : IPersonService
{
    private readonly IPersonRepository _repository;

    public PersonService(IPersonRepository repository)
    {
        _repository = repository;
    }

    public Person GetPerson(int id)
    {
        return _repository.GetPerson(id);
    }
}

public interface IPersonRepository
{
    Person GetPerson(int id);
}

public class PersonRepository : IPersonRepository
{
    private readonly int _serviceId;

    public PersonRepository(int serviceId)
    {
        _serviceId = serviceId;
    }

    public Person GetPerson(int id)
    {
        throw new System.NotImplementedException();
    }
}

Then the controller takes the PersonService in the constructor

 public class HomeController : Controller
{
    private readonly IPersonService _service;

    public HomeController(IPersonService service)
    {
        _service = service;
    }

    public ActionResult Index()
    {
        return View();
    }

}

Obviously this will fall over due to the container expecting the ServiceId argument on the constructor of PersonRepository with the following exception "Cannot resolve parameter 'Int32 serviceId'"

I can get the serviceId once I know HttpContext.Request.Current.Url, however this is not known at the time of creating the Container.

I have looked at many articles, forums etc but don't seem to be getting anywhere.

Could anyone point me in the right direction. Your help will be much appreciated.

Thanks

Answer 1

I know you use autofac but in our project we use Unity and it definitely can insert primitive types to type registration like this:

container.RegisterTypeWithParams<INewsRepository, NewsRepository>("ConnectionString", typeof(ILoggedUser));

Look at this

Answer 2

In general, you don't want to do this as you've modeled it (your PersonRepository). DI is used to resolve service dependencies, and what you have is a stateful component.

The way to model this is to use an abstract factory. Mark Seemann has an excellent blog post on this exact subject.

As you noted in your comment, passing the value via method injection is also an option, but can be ugly if it needs to be passed down through multiple dependencies.