Different behavior of FromKeyedServices attribute in Minimal APIs handler vs class library

[marcominerva]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

If we use the FromKeyedServices attribute in a class library and the keyed registration is missing, it falls back to the default dependency injection behavior and gets the last registered implementation (even with no key). However, If we use FromKeyedServices directly in a Minimal API endpoint handler and the key does not exist, it throws an exception.

Expected Behavior

The FromKeyedServices attribute should behave in the same way in every context.

Steps To Reproduce

Minimal repro here: https://github.com/marcominerva/KeyedServicesIssue

Exceptions (if any)

When using FromKeyedServices directly in a Minimal API endpoint handler:

System.InvalidOperationException: No service for type 'KeyedServicesIssue.Library.IDependency' has been registered.
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetRequiredKeyedService(Type serviceType, Object serviceKey, ServiceProviderEngineScope serviceProviderEngineScope)
at lambda_method2(Closure, Object, HttpContext)

When using FromKeyedServices in a class library, no exception at all is thrown, even if the key does not exist.

.NET Version

8.0.204

[captainsafia]

@marcominerva Thanks for reporting this!

The behavior that you're seeing is a consistent and intentional choice with all the implementations for keyed services in ASP.NET Core (SignalR, MVC, minimal APIs).

The expected pattern for resolving a service instance with any key using keyed DI is to take advantage of the KeyedService.AnyKey definition which is designed to match the behavior that you see here.

cc: @benjaminpetit For insights onto the behavior in the runtime's DI resolution strategy

[marcominerva]

So, to be sure to have understood the context, in the following case:

builder.Services.AddSingleton<SampleConfig>();

app.MapGet("api/sample-config", ([FromKeyedServices("x")] SampleConfig config) =>
{
    return TypedResults.Ok(config.Value);
});

This code throws an exception, because there isn't a SampleConifg instance that has been registered with the key x.

On the other hand, in the following scenario:

builder.Services.AddSingleton<SampleConfig>();
builder.Services.AddScoped<OtherSampleService>();

app.MapGet("api/external-sample-config", (OtherSampleService otherSampleService) =>
{
    return TypedResults.Ok(otherSampleService.ConfigValue);
})

public class OtherSampleService
{
    private readonly SampleConfig config;

    public OtherSampleService([FromKeyedServices("x")] SampleConfig config, IServiceProvider serviceProvider)
    {
        this.config = config;
    }

    public string ConfigValue => config.Value.ToString();
}

The code doesn't raise any exception and, even if OtherSampleService requires a SampleConfig with key x, because it doesn't exist, it gets the "default" registration.

[captainsafia]

So, to be sure to have understood the context, in the following case:

Yep, your understanding here is correct. I agree with you that the difference in behavior is a little strange so I've pinged @benjaminpetit above (who worked on the keyed services implementation) to get a sense of why the implementation behaves this way in constructor binding.

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[steveharter]

This should be fixed for v9.

[captainsafia]

@steveharter Thanks! Do you happen to know what preview the fix shipped in for verification?