MSDI Keyed Services

Microsoft Dependency Injection Keyed Services

Plugin for Microsoft.Extensions.DependencyInjection enabling registration of multiple service implementations under the same interface.

You can think about it as equivalent of Autofac Keyed Services or Ninject Named bindings.

How to use

Install package

dotnet add package MSDI.KeyedServices

Register service with one extensions method call passing key and registration action

public void ConfigureServices(IServiceCollection services)
{
    services.AddKeyedService<IGreeter, EnglishGreeter, Language>(
        key: Language.En, 
        registration: serviceCollection => 
        {
          serviceCollection.AddTransient<EnglishGreeter>();
        });
}

Or do it separately

services.AddKeyedService<IGreeter, PolishGreeter, Language>(key: Language.Pl, registration: null);
services.AddTransient<PolishGreeter>();

In both cases, remember to not wire implementation types with service they implement.

To resolve registered services you have two options

Dependency Injection via constructor

[ApiController]
public class GreetingsController : ControllerBase
{
    private readonly IKeyedServiceProvider<IGreeter, Language> _greeterProvider;

    public GreetingsController(IKeyedServiceProvider<IGreeter, Language> greeterProvider)
    {
        _greeterProvider = greeterProvider;
    }

    [HttpGet, Route("api/hello")]
    public IActionResult SayHello(string lang)
    {
        if (Enum.TryParse<Language>(lang, ignoreCase: true, result: out var language))
        {
            IGreeter greeter = _greeterProvider.GetKeyedService(language);
            string greetings = greeter.Greet();
            return Ok(greetings);
        }

        return BadRequest("Unknown language");
    }
}

To try it out for yourself, download this repository, run MSDI.KeyedServices.Example project and call http://localhost:59792/api/hello?lang=pl in your browser.

You can find presented examples in GreetingsController. Put some breakpoints and play around.

Service Locator

Sometime service locator pattern is a way to go.

Here is how you can use it with this library.

[HttpGet, Route("api/hello/en")]
public IActionResult SayHelloEn()
{
    var keyedServiceProvider =
        _serviceProvider.GetService(typeof(IKeyedServiceProvider<IGreeter, Language>)) 
        as IKeyedServiceProvider<IGreeter, Language>;

    IGreeter greeter = keyedServiceProvider.GetKeyedService(Language.En);

    string greetings = greeter.Greet();
    return Ok(greetings);
}