Services and Dependency Injection

Advanced Services and Dependency Injection in Angular Tutorial. Deep dive with production-oriented examples—not a shallow overview.

Architecture & mental model

Dependency injection in ASP.NET Core uses constructor injection by default. Register services in Program.cs with appropriate lifetimes: Singleton (stateless/cache), Scoped (per request, DbContext), Transient (lightweight helpers).

Implementation (production-style)

Type the code below; change names and types to match your domain. Compare with how Angular teams structure layers in mature codebases.

builder.Services.AddScoped();
builder.Services.AddDbContext(o =>
    o.UseSqlServer(builder.Configuration.GetConnectionString("Default")));

public class OrdersController : ControllerBase
{
    private readonly IOrderService _orders;
    public OrdersController(IOrderService orders) => _orders = orders;
}

Decision checklist

• Requirements: What are latency, consistency, and security needs for "Services and Dependency Injection"?
• Boundaries: Which layer owns this logic (UI, API, domain, infrastructure)?
• Failure modes: What happens when dependencies time out or return partial data?
• Observability: What logs or metrics prove this feature works in production?

Hands-on lab (45–60 min)

1. Reproduce the primary example for "Services and Dependency Injection" in a scratch project using Angular.
2. Add one automated test (unit or integration) that would fail if you break the core behavior.
3. Introduce a deliberate bug (wrong lifetime, missing await, wrong dependency order) and observe the symptom.
4. Document one trade-off you would present in a design review.

Pitfalls senior engineers avoid

• Capturing Scoped services in Singletons (captive dependency).
• Service locator anti-pattern via IServiceProvider everywhere.
• Registering DbContext as Singleton.

Interview depth

Question: Explain Services and Dependency Injection to a junior developer in 2 minutes, then list two trade-offs.

Strong answer: Start with the problem it solves, describe one real project usage, mention a failure you debugged or would test for, and close with alternatives (when not to use this approach).

Summary

You completed an advanced treatment of Services and Dependency Injection. Revisit after building a feature that uses it end-to-end; spaced repetition with real code beats re-reading alone.