How to register multiple implementations of the same interface in Asp.Net Core?

Question

I have services that are derived from the same interface.

public interface IService { }
public class ServiceA : IService { }
public class ServiceB : IService         


        

Answer 1

It is not supported by Microsoft.Extensions.DependencyInjection.

But you can plug-in another dependency injection mechanism, like StructureMap See it's Home page and it's GitHub Project.

It's not hard at all:

1. Add a dependency to StructureMap in your project.json:

   "Structuremap.Microsoft.DependencyInjection" : "1.0.1",
   

2. Inject it into the ASP.NET pipeline inside ConfigureServices and register your classes (see docs)

   public IServiceProvider ConfigureServices(IServiceCollection services) // returns IServiceProvider !
   {
       // Add framework services.
       services.AddMvc();
       services.AddWhatever();
   
       //using StructureMap;
       var container = new Container();
       container.Configure(config =>
       {
           // Register stuff in container, using the StructureMap APIs...
           config.For().Add(new Cat("CatA")).Named("A");
           config.For().Add(new Cat("CatB")).Named("B");
           config.For().Use("A"); // Optionally set a default
           config.Populate(services);
       });
   
       return container.GetInstance();
   }
   

3. Then, to get a named instance, you will need to request the IContainer

   public class HomeController : Controller
   {
       public HomeController(IContainer injectedContainer)
       {
           var myPet = injectedContainer.GetInstance("B");
           string name = myPet.Name; // Returns "CatB"
   

That's it.

For the example to build, you need

    public interface IPet
    {
        string Name { get; set; }
    }

    public class Cat : IPet
    {
        public Cat(string name)
        {
            Name = name;
        }

        public string Name {get; set; }
    }