dotnet-csharp-dependency-injection

To register multiple implementations in the .NET DI container, you can use collection registration patterns or factory delegates to resolve specific instances dynamically. Alternatively, .NET 8+ supports keyed services, allowing you to register and resolve multiple implementations of the same interface using distinct identifier keys.

Service lifetimes in ASP.NET Core dictate instance lifespan: Transient creates a new instance every time, Scoped creates one per request, and Singleton creates a single application-wide instance. Correctly applying these prevents captive dependency issues where long-lived services trap short-lived ones.

A Singleton service throwing an exception when resolving a Scoped DbContext indicates a captive dependency problem. In .NET dependency injection, a Singleton cannot safely depend on a Scoped service because the Scoped service becomes effectively trapped, leading to memory leaks and concurrency errors.

To implement the decoration pattern with Microsoft.Extensions.DependencyInjection, you wrap an existing registered service with a decorator class using factory delegates or the built-in activation utilities. This allows adding behavior like logging or caching without modifying the original implementation's code.

Yes, you can use keyed services in .NET 8 to resolve dependencies dynamically by registering types with a specific key. This advanced feature in the Microsoft.Extensions.DependencyInjection container allows selecting between multiple implementations of an interface at resolution time using the provided key.

To implement background tasks using hosted services in ASP.NET Core, you register a class implementing IHostedService or BackgroundService in the DI container. The application automatically starts and stops these services, managing long-running operations independently of web requests.