C# IServiceProvider and Dependency Injection ambiguous interface

Question

I would like to use Microsoft's dependency injection extension to achieve DI. I have created a simple console application to test out my understanding. I have 2 objects, Dog and Cat both have a interface IAnimal. Very simple setup. I wanted to use AddTranient<IAnimal, Dog> and AddTranient<IAnimal, Cat> to create the service that houses my Dog and Cat object. Later when I retrieve objects, I am running into issues using GetRequiredService(). It only returns the last object Cat. See below code using .Net 6. How do I retrieve Dog object when I needed and vise versa for Cat object?

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
builder.Services.AddTransient<IAnimal, Dog>();
builder.Services.AddTransient<IAnimal, Cat>();

using IHost host = builder.Build();

var myobject = GetAnimalObject(host.Services, "Scope 1");
Console.WriteLine($"Name: {myobject.name}");
await host.RunAsync();

static IAnimal GetAnimalObject(IServiceProvider services, string scope)
{
    using IServiceScope serviceScope = services.CreateScope();
    IServiceProvider provider = serviceScope.ServiceProvider;
    var result = provider.GetRequiredService<IAnimal>();
    return result;
}

public sealed class Dog : IAnimal
{
    public string name { get; set; } = "Daug";
}

public sealed class Cat : IAnimal
{
    public string name { get; set; } = "Kate";
}

public interface IAnimal
{
    string name { get; set; }
}

I tried GetRequiredService and GetRequiredService but both returned null.

Answer 1

It's normal for .NET's DI to return the last registered service. This allows other services to "override" the previous services.

To get all services for an interface, call GetServices<IAnimal> instead of GetRequiredService<IAnimal>. GetServices will return an IEnumerable<IAnimal> of all the services.