All 16 Dependency Injection questions
More in Dependency Injection
How do third-party DI containers like Autofac integrate with ASP.NET Core's built-in DI abstractions? How does ASP.NET Core's DI container support injecting a logger via ILogger<T>, and how is the generic type parameter used? What is dependency injection, and why does it make a codebase easier to test and maintain? What is the 'captive dependency' problem, and how does the DI container help catch it? How do you use IServiceScopeFactory to manually create and manage a DI scope outside the normal request pipeline? How does the DI container's disposal behavior work for IDisposable and IAsyncDisposable services across different lifetimes? What is the Options pattern's relationship to DI, and how does IOptions<T> itself get resolved through the container? How would you unit test a service that depends on multiple injected interfaces without spinning up the full DI container?
Advertisement
Back to results for “Dependency Injection”
.NET › Dependency Injection

What are keyed services (introduced in .NET 8), and what problem do they solve compared to multiple unnamed registrations?

Advanced

Answer

Keyed services let you register multiple implementations of the same interface under distinct string or object keys, then resolve a specific one explicitly using [FromKeyedServices("key")] or GetRequiredKeyedService(key) -- solving the ambiguity problem of IEnumerable<T> injection (which gives you everything, requiring you to filter or iterate) when you actually need one specific, named implementation deterministically, without resorting to a factory pattern or string-based service locator anti-pattern.
builder.Services.AddKeyedScoped<IPaymentProcessor, StripeProcessor>("stripe");
builder.Services.AddKeyedScoped<IPaymentProcessor, PayPalProcessor>("paypal");

public class CheckoutService {
    public CheckoutService([FromKeyedServices("stripe")] IPaymentProcessor processor) {
        _processor = processor;  // explicitly gets the Stripe implementation
    }
}
Real-world example A multi-payment-provider e-commerce platform uses keyed services to explicitly wire different checkout flows to specific payment processors (stripe, paypal, applepay) without needing a custom factory class or dictionary-based lookup that keyed services now handle natively.

Common follow-ups: How do keyed services interact with IEnumerable<T> injection -- can you still get all of them?;What's the migration path from a hand-rolled factory pattern to keyed services?

Configuration & Options;RESTful Web APIs & Controllers
All 16 Dependency Injection questions