每个会话在Autofac中向接口注册不同的类？

Question

What I'm asking may not be possible/recommended, but I couldn't find anything on it online. Feel free to point me in a different direction.

What I'm trying to accomplish:

Register different Classes to an Interface in Autofac conditionally - per user session

For example, I'd like to take my current implementation:

var builder = new ContainerBuilder();
builder.RegisterControllers(Assembly.GetExecutingAssembly());
builder.RegisterType(typeof(RunHistoryRepository))
       .As(typeof(IRunHistoryRepository));

And add something like:

var builder = new ContainerBuilder();
builder.RegisterControllers(Assembly.GetExecutingAssembly());
if(UserIsInThisRole())
  builder.RegisterType(typeof(RunHistoryRepository))
         .As(typeof(IRunHistoryRepository));
else
    builder.RegisterType(typeof(DifferentRunHistoryRepository))
           .As(typeof(IRunHistoryRepository));

What I know:

This code is called from the Global.asax, so this will run only when the site is started. Because of this, I feel like this logic can't/shouldn't go here...

What I've tried:

I've tried the above implementation and it doesn't work since this code runs on application start - not each user visit. I've also looked into registering these types with parameters (and then I could modify the RunHistoryRepository logic to select a data source conditionally):

builder.RegisterType<RunHistoryRepository>()
   .As<IRunHistoryRepository>()
   .WithParameter("DataSource", "DataSource1Key");

But I would need the parameter to be dynamic on user visit:

builder.RegisterType<RunHistoryRepository>()
   .As<IRunHistoryRepository>()
   .WithParameter("DataSource", UserDataSource());

And again, since this executes from the Global.asax it will register before a user even hits the page.

Is it possible to register these types dynamically for each user that visits the site or do I need to handle this logic elsewhere?

Answer 1

There's a couple of options here. You can register functions in the container that will be executed every time you ask for a service to be resolved

var builder = new ContainerBuilder();
builder
    .Register<Func<bool, IRunHistoryRepository>>(
        x =>
        {
            var context = x.Resolve<IComponentContext>();
            return isUserInRole => 
            {
                return isUserInRole
                    ? context.Resolve<RunHistoryRepository>()
                    : context.Resolve<DifferentRunHistoryRepository>();
            }
        }
)};

You can also use Named and Keyed Services to resolve implementations via an enum or string.

To throw out a curveball, I've recently been registering components ' on the fly ' within a nested lifetime scope.

// a component that uses IOwinContext as a dependency
class CommandHandler
{
    // this IOwinContext will be a different instance for each HttpRequest
    readonly IOwinContext _context;

    public CommandHandler(IOwinContext context)
    {
        _context = context;
    }
}

// capture our HttpRequest via the IOwinContext object
var context = ...

// create a nested scope
using (var scope = Container.BeginLifetimeScope(builder =>
{
    // register the Owin context for this specific HttpRequest
    builder.RegisterInstance(context).As<IOwinContext>();
}))
{
    // this component will be resolved with the specific IOwinContext
    // that we registered above
    var handler = scope.Resolve<CommandHandler>();
}

Answer 2

You can register your service with a named service and register a factory using a delegate that will resolved the named service based on your condition :

builder.RegisterType(typeof(RunHistoryRepository))
       .Named<IRunHistoryRepository>("standard");
builder.RegisterType(typeof(DifferentRunHistoryRepository))
       .Named<IRunHistoryRepository>("different");

builder.Register(c => {
   if(UserIsInThisRole()) {
       return c.ResolveNamed<IRunHistoryRepository>("different"); 
   } else {
       return c.ResolveNamed<IRunHistoryRepository>("standard"); 
   }
})
.As<IRunHistoryRepository>(); 

By the way, I recommend you not to have if(UserIsInThisRole()) in the delegate but rely on another service that will do the check for you.

if(c.Resolve<IRoleManager>().IsInRole("xxx"))