How do I register and resolve multiple implementations for a service?

Question

Can I register multiple implementations of a given service interface?

services.AddTransient<ISerivce, Service1>();
services.AddTransient<ISerivce, Service2>();
services.AddTransient<ISerivce, Service3>();

And, then, how do I inject or resolve all of the registered implementations in an array or list?

var services = myTypedFactory.ResolveAll();
myCustomFactory.Release(services);

So you want to create a factory around the resolving of the services? The asp.net core DI is able to allow resolve using services.GetService<IEnumerable<IService>> out of the box — Martin Ullrich
– Martin Ullrich, Commented Oct 26, 2017 at 19:31
@MartinUllrich is this documented anywhere? it's been 3 years and I still can't find any relevant docs! — Anthony Mastrean
– Anthony Mastrean, Commented Jun 24, 2020 at 16:36

Anthony Mastrean · Accepted Answer · 2020-06-24 16:38:44Z

6

Given multiple registrations in Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IService, ServiceA>();
    services.AddTransient<IService, ServiceB>();
    services.AddTransient<IService, ServiceC>();
}

You should be able to depend on an IEnumerable<TService> in the depending service.

public Foo(IEnumerable<IService> services)
{
    this.services = services;
}

This does not appear to be documented yet, although, strangely, the opposite behavior is documented as the TryAdd* methods.

answered Jun 24, 2020 at 16:38

Anthony Mastrean

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5 Comments

Stephan Schinkel Over a year ago

Note: IList<T> or IService[] does not work. IEnumerable<T> is the only way to go.

BendEg Over a year ago

@StephanSchinkel thanks! Do you know if there is any reason why?

Stephan Schinkel Over a year ago

@BendEg: i assume -> Performance. But This knowledge is nearly 3,5 years old. Take everything with a grain of Salt. .net has undergone some serious refactorings since then.

BendEg Over a year ago

@StephanSchinkel it is still only working with IEnumerable<> i will research why, thanks!

Sarin Over a year ago

This behavior is now documented Dependency injection in ASP.NET Core: Service registration methods and .NET dependency injection: Service registration methods

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