ASP.NET Core Interview Question #62

What is keyed dependency injection in ASP.NET Core?

Dependency Injection & Services Junior Beginner

Quick Interview Answer

Keyed dependency injection allows multiple implementations of the same service type to be registered and selected by a key. This is useful when an application has several strategies that implement one interface.

Detailed Explanation

Modern .NET provides keyed service registration methods such as AddKeyedScoped, AddKeyedTransient, and AddKeyedSingleton. A consumer can request a keyed implementation using FromKeyedServices or keyed resolution APIs.

Keys should represent a meaningful selection rule. If selection logic becomes complex, a strategy resolver or factory may provide a cleaner domain abstraction.

Code Example

builder.Services.AddKeyedScoped<INotificationSender, EmailSender>("email");
builder.Services.AddKeyedScoped<INotificationSender, SmsSender>("sms");

public class AlertsController : Controller
{
    public AlertsController(
        [FromKeyedServices("email")] INotificationSender sender)
    {
        _sender = sender;
    }

    private readonly INotificationSender _sender;
}