Interview Q&A

Short answer: IServiceProvider: Resolves services manually. IServiceScopeFactory: Creates a new DI scope (useful for background tasks). using (var scope = serviceScopeFactory.CreateScope())

Example code

{
var scopedService = scope.ServiceProvider.GetRequiredService<IMyScopedService>(); }

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Middleware logs incoming requests; action filter logs controller-level execution.

Real-world example (ShopNest)

ShopNest pipeline order matters: exception handling → HTTPS → auth → authorization → endpoints. Auth must run before protected APIs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Scoped services are tied to the HTTP request lifecycle. In background tasks, you must manually create a scope using IServiceScopeFactory to resolve scoped services safely.

Real-world example (ShopNest)

ShopNest registers AppDbContext as Scoped and IMemoryCache as Singleton. Putting DbContext in a Singleton causes threading bugs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Mixing sync & async can cause deadlocks. Prefer async filters.

Real-world example (ShopNest)

A ShopNest ValidateModelAttribute runs before actions and returns 400 if ModelState is invalid—same rule for every controller.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: To replace: services.AddSingleton<IService, CustomImplementation>(); To remove: var descriptor = services.First(x => x.ServiceType == typeof(IMyService)); services.Remove(descriptor);

Real-world example (ShopNest)

ShopNest registers AppDbContext as Scoped and IMemoryCache as Singleton. Putting DbContext in a Singleton causes threading bugs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Yes—but avoid heavy operations that run per action.

Real-world example (ShopNest)

ShopNest registers AppDbContext as Scoped and IMemoryCache as Singleton. Putting DbContext in a Singleton causes threading bugs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: IOptionsMonitor) IOptions<T>: For singleton/config services. IOptionsSnapshot<T>: Scoped; updates per request. IOptionsMonitor<T>: Singleton; can react to config changes. services.Configure<MySettings>(Configuration.GetSection("MySettings" ));

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use IOptions or DI into constructor.

Real-world example (ShopNest)

A ShopNest ValidateModelAttribute runs before actions and returns 400 if ModelState is invalid—same rule for every controller.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: there Use IHostedService or BackgroundService for tasks that run in the background. Services are injected via constructor. Scoped services must use IServiceScopeFactory.

Real-world example (ShopNest)

ShopNest registers AppDbContext as Scoped and IMemoryCache as Singleton. Putting DbContext in a Singleton causes threading bugs.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: When exceptions must be caught outside MVC (e.g., authorization failures).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: IConfiguration is automatically registered and injected via constructor. public MyService(IConfiguration config)

Example code

{
var key = config["MyKey"];
}

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: dd custom validation and authorization filters using .AddEndpointFilter().

Real-world example (ShopNest)

A ShopNest ValidateModelAttribute runs before actions and returns 400 if ModelState is invalid—same rule for every controller.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: ASP.NET Core provides structured logging via ILogger<T>. public class MyService

Example code

{
private readonly ILogger<MyService> _logger;
public MyService(ILogger<MyService> logger) => _logger = logger;
public void DoSomething() => _logger.LogInformation("Action performed"); }

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Yes—result filters can wrap or modify responses.

Real-world example (ShopNest)

A ShopNest ValidateModelAttribute runs before actions and returns 400 if ModelState is invalid—same rule for every controller.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Occurs when two services depend on each other directly or indirectly. 🛠 Fix: Refactor to remove circular reference Use Lazy<T> or factory injection Split responsibilities

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: A filter that tracks performance of controller actions: public class ProfilingFilter : IAsyncActionFilter

Example code

{
public async Task OnActionExecutionAsync( ActionExecutingContext context, ActionExecutionDelegate next) {
var sw = Stopwatch.StartNew();
var result = await next(); sw.Stop(); Console.WriteLine($"Action took {sw.ElapsedMilliseconds}ms"); }
}

Real-world example (ShopNest)

A ShopNest ValidateModelAttribute runs before actions and returns 400 if ModelState is invalid—same rule for every controller.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Use a mocking framework like Moq: var mockService = new Mock<IMyService>(); mockService.Setup(s => s.Get()).Returns("test"); var controller = new MyController(mockService.Object); Mocking helps isolate the unit of work and test behavior independently. MVC & Razor Pages

Example code

Use a mocking framework like Moq: var mockService = new Mock<IMyService>();
mockService.Setup(s => s.Get()).Returns("test");
var controller = new MyController(mockService.Object); Mocking helps isolate the unit of work and test behavior independently. MVC & Razor Pages

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: MVC (Model-View-Controller) is a pattern for organizing code into: Model: Data and business logic View: UI rendering Controller: Input handling and app flow Built on a modular, cross-platform framework. Uses dependency injection by default. Unified Web API + MVC pipeline. Lightweight and middleware-based request processing.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: How does it differ from MVC in “older” ASP.NET? MVC (Model-View-Controller) is a pattern for organizing code into: Model: Data and business logic View: UI rendering Controller: Input handling and app flow Built on a modular, cross-platform framework. Uses dependency injection by default. Unified Web API + MVC pipeline. Lightweight and middleware-based request processing.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: SP.NET Core 2.0. Each .cshtml file has an associated PageModel class (like a view + controller combined). Best for simple UI-focused apps or CRUD pages. ✅ Use Razor Pages for: Simpler, page-focused apps ✅ Use MVC for: Complex, controller-based routing or large, structured apps

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: When to use Razor Pages instead of MVC? Razor Pages is a page-based programming model introduced in ASP.NET Core 2.0. Each .cshtml file has an associated PageModel class (like a view + controller combined). Best for simple UI-focused apps or CRUD pages. ✅ Use Razor Pages for: Simpler, page-focused apps ✅ Use MVC for: Complex, controller-based routing or large, structured apps

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: MVC Routing: Uses attribute routing or conventional routing.

Example code

endpoints.MapControllerRoute( name: "default", pattern: "{controller=Home}/{action=Index}/{id?}"); Razor Pages Routing: Based on folder structure. URL /Products/Edit maps to /Pages/Products/Edit.cshtml.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: }"); Razor Pages Routing: Based on folder structure. URL /Products/Edit maps to /Pages/Products/Edit.cshtml.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: view or JSON). View: .cshtml file that renders HTML. View Component: Reusable mini-views with logic (like partials but with code-behind).

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.

Short answer: Controller: Handles HTTP requests. Action Method: A method in the controller that returns a result (like a view or JSON). View: .cshtml file that renders HTML. View Component: Reusable mini-views with logic (like partials but with code-behind).

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.