Asp.Net Interview Questions and Answers

1. What is the difference between IQueryable and IEnumerable in ASP.NET?

Answer:

• IEnumerable: It is an interface that represents a collection that can be enumerated. When you use IEnumerable, data is retrieved in-memory, meaning it fetches all data from the database into memory before processing.

• IQueryable: It represents a query that can be executed against a data source (usually a database). IQueryable supports deferred execution, meaning the query is executed when you iterate over it or materialize it.

2. What is the importance of middleware in ASP.NET Core?

Answer:
Middleware in ASP.NET Core handles HTTP requests and responses. Each middleware in the pipeline can either handle the request or pass it on to the next middleware. Middleware is used for tasks such as logging, authentication, error handling, and routing. Middleware enables building a modular and maintainable request pipeline.

3. How do you implement custom authentication and authorization in ASP.NET Core?

Answer:
Custom authentication can be implemented by creating a custom authentication handler that derives from AuthenticationHandler<TOptions>. Similarly, custom authorization can be implemented by creating custom authorization policies or custom authorization handlers. You register these handlers in the ConfigureServices method and apply them via attributes like [Authorize].

public class CustomAuthenticationHandler : AuthenticationHandler<AuthenticationSchemeOptions> { public CustomAuthenticationHandler(IOptionsMonitor<AuthenticationSchemeOptions> options, ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock) : base(options, logger, encoder, clock) { } protected override Task<AuthenticateResult> HandleAuthenticateAsync() { // Implement custom authentication logic } }

4. What is the ConfigureServices method in Startup.cs and how is it used?

Answer:
The ConfigureServices method is where all services required by the application (such as database contexts, identity services, authentication handlers, etc.) are configured. You register services in the dependency injection (DI) container here, making them available throughout the application.

Example:

public void ConfigureServices(IServiceCollection services) { services.AddDbContext<MyDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"))); services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme) .AddCookie(options => { options.LoginPath = "/Account/Login"; }); }

5. What is the significance of async and await in ASP.NET Core?

Answer:
The async and await keywords are used to write asynchronous code in C#. They enable non-blocking operations, such as database calls or HTTP requests, to run in the background, allowing the application to remain responsive. async marks a method as asynchronous, and await is used to pause execution until the awaited task completes.

Example:

public async Task<IActionResult> GetData() { var data = await _dataService.GetDataAsync(); return Ok(data); }

6. What are background services in ASP.NET Core, and how do you implement them?

Answer:
Background services in ASP.NET Core are long-running tasks that run outside the HTTP request-response cycle. You can implement background services by creating a class that implements the IHostedService interface. These services are useful for jobs like polling, cleanup tasks, or sending emails.

Example:

public class BackgroundService : IHostedService { public Task StartAsync(CancellationToken cancellationToken) { // Start background task } public Task StopAsync(CancellationToken cancellationToken) { // Stop background task } }

7. How do you prevent Cross-Site Scripting (XSS) attacks in ASP.NET?

Answer:
Cross-Site Scripting (XSS) attacks can be prevented by:

• Encoding output: Always encode output before rendering it in views to prevent malicious scripts from executing.

• Using anti-XSS libraries: ASP.NET Core automatically encodes output by default using the Razor view engine.

• Content Security Policy (CSP): Use a strict CSP header to restrict the sources from which scripts can be loaded.

@Html.Encode(model.Name) // Prevents XSS by encoding input

8. What are the benefits and drawbacks of using Entity Framework Core (EF Core) in production environments?

Answer:

• Benefits: EF Core simplifies database access through LINQ queries and provides automatic change tracking, migrations, and supports multiple database providers (SQL Server, SQLite, PostgreSQL, etc.).

• Drawbacks: EF Core can have performance overhead due to automatic change tracking and complex queries. It might not be ideal for scenarios where fine-tuned performance or complex queries are necessary.

9. What is Dependency Injection (DI) and how is it used in ASP.NET Core?

Answer:
Dependency Injection is a design pattern used to decouple classes and their dependencies, making it easier to manage dependencies. In ASP.NET Core, DI is built into the framework, and services can be registered in ConfigureServices. It promotes better testability and modular code.

Example:

public void ConfigureServices(IServiceCollection services) { services.AddSingleton<IMyService, MyService>(); }

10. What is the purpose of the HttpClientFactory in ASP.NET Core?

Answer:
HttpClientFactory provides a central place for configuring and managing HttpClient instances. It helps avoid common issues such as socket exhaustion when making multiple HTTP requests. It also allows you to centralize the configuration, such as base URLs and headers, for all outgoing HTTP requests.

Example:

public void ConfigureServices(IServiceCollection services) { services.AddHttpClient("MyClient", c => { c.BaseAddress = new Uri("https://api.example.com"); c.DefaultRequestHeaders.Add("Accept", "application/json"); }); }

11. How does routing work in ASP.NET Core MVC?

Answer:
In ASP.NET Core MVC, routing is responsible for mapping an HTTP request to a controller and action method. The routing system uses patterns defined in the Configure method of Startup.cs to match incoming requests to the correct controller and action.

Example:

app.UseEndpoints(endpoints => { endpoints.MapControllerRoute( name: "default", pattern: "{controller=Home}/{action=Index}/{id?}"); });

12. What is the difference between ViewData, ViewBag, and TempData?

Answer:

• ViewData: A dictionary used to pass data between controllers and views. It is cleared after each request.

• ViewBag: A dynamic wrapper around ViewData that allows passing data from controllers to views using properties.

• TempData: Stores data that needs to persist across requests, typically used to pass data during a redirect.

13. How do you perform unit testing in ASP.NET Core?

Answer:
Unit testing in ASP.NET Core can be done by testing the controller actions or service methods independently. You can use mock objects to simulate dependencies and verify the behavior of your code.

Example using Moq:

public class MyServiceTests { [Fact] public void GetData_ReturnsCorrectData() { var mockService = new Mock<IMyService>(); mockService.Setup(s => s.GetData()).Returns(new List<string> { "Test" }); var controller = new MyController(mockService.Object); var result = controller.GetData(); Assert.Equal("Test", result.First()); } }

14. How do you implement versioning in ASP.NET Core Web API?

Answer:
API versioning in ASP.NET Core can be done by adding versioning logic to your controllers or routes. You can use libraries such as Microsoft.AspNetCore.Mvc.Versioning to handle versioning.

Example:

public void ConfigureServices(IServiceCollection services) { services.AddApiVersioning(options => { options.ReportApiVersions = true; options.AssumeDefaultVersionWhenUnspecified = true; }); }

15. What are the different ways to handle errors in ASP.NET Core?

Answer:

• Exception Handling Middleware: Use UseExceptionHandler() to handle global exceptions and return custom error pages.

• Try-Catch: Handle exceptions locally in controllers or services.

• Custom Error Pages: Customize error pages for different HTTP status codes, such as 404 or 500.

Example:

app.UseExceptionHandler("/Home/Error");

16. What is the IActionResult interface and how is it used in ASP.NET Core MVC?

Answer:
IAction Result is the base interface for all result types returned by action methods in ASP.NET Core MVC. It can represent views, HTTP responses, status codes, or JSON data. Common implementations include ViewResult, JsonResult, RedirectResult, and StatusCodeResult.

Example:

public IActionResult Index() { return View(); }

17. How do you manage session state in ASP.NET Core?

Answer:
In ASP.NET Core, session state is managed through cookies, and it is configured using the AddSession() method in ConfigureServices. Session data can be stored in-memory, Redis, or a database.

Example:

public void ConfigureServices(IServiceCollection services) { services.AddSession(options => { options.Cookie.HttpOnly = true; }); }

18. What are the new features in ASP.NET Core 5/6?

Answer:
ASP.NET Core 5 and

6 introduced features like minimal APIs, improved performance, better integration with Blazor, enhanced support for SignalR, and improved support for WebAssembly. ASP.NET Core 6 is a Long-Term Support (LTS) version, offering additional improvements like enhanced route handling and integration with cloud-native services.

19. What is SignalR, and how do you implement real-time communication in ASP.NET Core?

Answer:
SignalR is a library for adding real-time web functionality to applications. It allows server-side code to send asynchronous notifications to client-side web applications. SignalR is used for scenarios like chat applications, live notifications, and real-time dashboards.

Example:

public class MyHub : Hub { public async Task SendMessage(string message) { await Clients.All.SendAsync("ReceiveMessage", message); } }

20. Explain the AddSingleton, AddScoped, and AddTransient lifetimes in ASP.NET Core dependency injection.

Answer:

• AddSingleton: The service is created once and shared throughout the application.

• AddScoped: A new instance is created per HTTP request.

• AddTransient: A new instance is created every time the service is requested.