Make GetKeyedServices(KeyedService.AnyKey) return all services

[stephentoub]

I expected GetKeyedServices(KeyedService.AnyKey) to return all services, since AnyKey is documented as "Gets a key that matches any key." This changes the behavior of KeysMatch accordingly.

Feel free to say "this isn't the right answer" if there's a better answer.

[ghost]

Tagging subscribers to this area: @dotnet/area-extensions-dependencyinjection
See info in area-owners.md if you want to be subscribed.

Issue Details

---

I expected GetKeyedServices(KeyedService.AnyKey) to return all services, since AnyKey is documented as "Gets a key that matches any key." This changes the behavior of KeysMatch accordingly.

Feel free to say "this isn't the right answer" if there's a better answer.

Author:	stephentoub
Assignees:	-
Labels:	area-Extensions-DependencyInjection
Milestone:	-

[skyoxZ]

Is there any docs/comments that let users learn that a magic value KeyedService.AnyKey can be used on relative Add/Get methods?

[benjaminpetit]

We need first to decide what to do when there is a KeyedService.AnyKey service registration. Currently with your PR, it does this:

var service1 = new Service();
var service2 = new Service();
var service3 = new Service();
var service4 = new Service();
var service5 = new Service();
var service6 = new Service();
var anyService = new Service();
var serviceCollection = new ServiceCollection();
serviceCollection.AddKeyedSingleton<IService>(KeyedService.AnyKey, anyService);
serviceCollection.AddKeyedSingleton<IService>("first-service", service1);
serviceCollection.AddKeyedSingleton<IService>("service", service2);
serviceCollection.AddKeyedSingleton<IService>("service", service3);
serviceCollection.AddKeyedSingleton<IService>("service", service4);
serviceCollection.AddKeyedSingleton<IService>(null, service5);
serviceCollection.AddSingleton<IService>(service6);

var provider = CreateServiceProvider(serviceCollection);

var allServices = provider.GetKeyedServices<IService>(KeyedService.AnyKey).ToList(); // returns only anyService

I don't think that's what we want?

[stephentoub]

We need first to decide what to do when there is a KeyedService.AnyKey service registration

I still don't fully understand when I would want one of those and so don't have a good answer for what it should mean when there is one.

[benjaminpetit]

Pinging @davidfowl

For example, you could do something like this:

serviceCollection.AddKeyedTransient<ILogger>(KeyedService.AnyKey, (sp, key) =>
{
    var factory = sp.GetRequiredService<ILoggerFactory>();
    return factory.CreateLogger(key.ToString());
});

And then in your class:

public class Service()
{
    public Service([FromKeyedServices("SomeCategory") ILogger logger]) { }
}

EDIT: plus, I don't think GetKeyedServices<IService>(KeyedService.AnyKey) should return non-keyed services too.

Also, right now if you have:

serviceCollection.AddKeyedSingleton<IService>("a", serviceA);
serviceCollection.AddKeyedSingleton<IService>(KeyedService.AnyKey, anyService);

then calling GetKeyedService<IService>("a") will return anyService, I also don't think it's correct.

[davidfowl]

then calling GetKeyedService("a") will return anyService, I also don't think it's correct.

That is fine if AnyKey means any key including the anykey itself no?

[stephentoub]

For example

Thanks, I understand it better now.

plus, I don't think GetKeyedServices(KeyedService.AnyKey) should return non-keyed services too.

Why? It returns them today if you pass null as the key, e.g. this prints 3:

using Microsoft.Extensions.DependencyInjection;

var c = new ServiceCollection();
c.AddSingleton<IService>(new Service("1"));
c.AddSingleton<IService>(new Service("2"));
c.AddKeyedSingleton<IService>(null, new Service("3"));
var p = c.BuildServiceProvider();

Console.WriteLine(p.GetKeyedServices<IService>(null).Count());

interface IService { }
record Service(string Name) : IService { }

null is valid in the domain of keys, so I don't know why it would be considered special here for the purposes of AnyKey.

Taking a step back, @benjaminpetit, we need a backportable solution to enumerating all of the instances. I don't particularly care whether it's GetServices<T>() or GetKeyedServices<T>(AnyKey), and I don't have strong views on what the behavior should be when AnyKey is used during registration. Can you help drive to a solution? If this PR isn't the answer, happy to close it and you can submit a replacement, or if there's a small change you'd like me to make, happy to do that, too. We just need a solution soon.

[benjaminpetit]

That is fine if AnyKey means any key including the anykey itself no?

Maybe? After some thoughts, ss long as we document it, I think both solutions are fine.

Why? It returns them today if you pass null as the key, e.g. this prints 3:

Because collection.AddKeyedSingleton<IService, Service>(null) and collection.AddSingleton<IService, Service>() are considered equivalent, same thing for collection.GetKeyedService<IMyService>(null) and collection.GetService<IMyService>().

A service with a null key is equivalent as a non-keyed service.

IMO the correct behavior would be: GetKeyedServices<T>(KeyedService.AnyKey) shoud return all the explicitely registered services, not the one that were "created" with AnyKey:

serviceCollection.AddKeyedSingleton<IMyService, MyService>(KeyedService.AnyKey);
serviceCollection.AddKeyedSingleton<IMyService, MyOtherService>("another_key");
 
var serviceProvider = serviceCollection.BuildServiceProvider();

// Will return two services, one with key "KeyedService.AnyKey", the other with "another_key"?
var services1 = serviceProvider.GetKeyedServices<IMyService>(KeyedService.AnyKey);
 
// Returns "MyService" -- thanks to the KeyedService.AnyKey registration
_ = serviceProvider.GetKeyedService<IMyService>("something_else");
 
// Returns two services, same as service1
var services2 = serviceProvider.GetKeyedServices<IMyService>(KeyedService.AnyKey);
 
// What should it return? To be consistent with what was returned in services2, nothing?
var services3 = serviceProvider.GetKeyedServices<IMyService>("plop");

What we choose to do for services2 and services3 will really impact this PR.

And maybe we should add another method like this (probaby for 9?):

IEnumerable<(object key, T service)> GetKeyedServices<T>();

I imagine that some people would be interested to get the key too.

[stephentoub]

Because collection.AddKeyedSingleton<IService, Service>(null) and collection.AddSingleton<IService, Service>() are considered equivalent, same thing for collection.GetKeyedService(null) and collection.GetService().

That's my point. GetKeyedServices(null) returns services registered without a key. And null is a valid value for a key. So I expect GetKeyedServices(AnyKey) to include null keys and therefor things registered without keys. It would otherwise be inconsistent.

[stephentoub]

Closing in favor of #95582