15 .NET 6 Interview Questions and Answers

.NET 6 is the latest iteration of Microsoft’s .NET platform, offering a unified framework for building applications across various environments, including web, mobile, desktop, and cloud. It brings significant performance improvements, new features, and enhanced developer productivity tools, making it a crucial skill for modern software development. With its cross-platform capabilities and extensive library support, .NET 6 is a versatile and powerful tool for developers.

This article provides a curated selection of interview questions designed to help you demonstrate your proficiency in .NET 6. By reviewing these questions and their detailed answers, you can better prepare for technical interviews, showcasing your understanding of the framework and its applications.

.NET 6 Interview Questions and Answers

1. Explain how middleware works in an ASP.NET Core application.

Middleware in an ASP.NET Core application consists of components that handle HTTP requests and responses in a specific order. Each component can perform operations before and after the next component in the pipeline is invoked, allowing for a clean separation of concerns. Middleware is configured in the Startup class, specifically in the Configure method, using the IApplicationBuilder interface.

Example:

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.Use(async (context, next) =>
        {
            // Do work before the next middleware
            await next.Invoke();
            // Do work after the next middleware
        });

        app.UseMiddleware<CustomMiddleware>();

        app.Run(async (context) =>
        {
            await context.Response.WriteAsync("Hello, World!");
        });
    }
}

public class CustomMiddleware
{
    private readonly RequestDelegate _next;

    public CustomMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        // Custom logic before the next middleware
        await _next(context);
        // Custom logic after the next middleware
    }
}

In this example, the Startup class configures the middleware pipeline. The app.Use method adds an inline middleware component, while app.UseMiddleware<CustomMiddleware> adds a custom middleware class. The app.Run method adds a terminal middleware that handles the request and generates a response.

2. Demonstrate how to implement dependency injection in a .NET 6 application.

Dependency Injection (DI) in .NET 6 allows for better modularity and easier testing by decoupling the creation of an object from its dependencies. To implement DI, define the service interface and its implementation, register the service in the DI container, and inject the service into the consuming class.

Example:

// Step 1: Define the service interface and its implementation
public interface IGreetingService
{
    string Greet(string name);
}

public class GreetingService : IGreetingService
{
    public string Greet(string name)
    {
        return $"Hello, {name}!";
    }
}

// Step 2: Register the service in the dependency injection container
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddTransient<IGreetingService, GreetingService>();

var app = builder.Build();

// Step 3: Inject the service into the consuming class
app.MapGet("/", (IGreetingService greetingService) =>
{
    return greetingService.Greet("World");
});

app.Run();

In this example, we define an IGreetingService interface and its implementation GreetingService. We then register the service with the DI container using AddTransient, which specifies that a new instance of the service will be created each time it is requested. Finally, we inject the IGreetingService into a minimal API endpoint.

3. Write a method that uses nullable reference types to avoid null reference exceptions.

Nullable reference types in .NET 6 allow developers to specify whether a reference type can be null, helping to avoid null reference exceptions by providing compile-time warnings.

Example:

#nullable enable

public class UserService
{
    public string? GetUserName(int userId)
    {
        string? userName = FetchUserNameFromDatabase(userId);
        
        if (userName == null)
        {
            return "Unknown User";
        }
        
        return userName;
    }

    private string? FetchUserNameFromDatabase(int userId)
    {
        return userId == 1 ? "John Doe" : null;
    }
}

#nullable disable

In this example, the GetUserName method returns a nullable string (string?). The method checks if the fetched user name is null and returns a default value if it is.

4. Show how to use one of the new LINQ enhancements introduced in .NET 6.

One of the new LINQ enhancements in .NET 6 is the MaxBy and MinBy methods, which find the maximum or minimum element in a sequence based on a specified key selector function.

Example:

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        var people = new List<Person>
        {
            new Person { Name = "Alice", Age = 30 },
            new Person { Name = "Bob", Age = 25 },
            new Person { Name = "Charlie", Age = 35 }
        };

        var oldestPerson = people.MaxBy(p => p.Age);
        var youngestPerson = people.MinBy(p => p.Age);

        Console.WriteLine($"Oldest: {oldestPerson.Name}, Age: {oldestPerson.Age}");
        Console.WriteLine($"Youngest: {youngestPerson.Name}, Age: {youngestPerson.Age}");
    }
}

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

5. Define a record type and explain its benefits over traditional classes.

A record type in .NET 6 is a reference type that provides built-in functionality for encapsulating data. Unlike traditional classes, records are immutable by default and provide value-based equality.

Example:

public record Person(string FirstName, string LastName);

var person1 = new Person("John", "Doe");
var person2 = new Person("John", "Doe");

Console.WriteLine(person1 == person2); // True

Benefits of using record types include immutability, value-based equality, concise syntax, and built-in functionality for cloning and with-expressions.

6. Implement a simple source generator that generates a class with properties.

Source generators in .NET 6 allow developers to generate additional source code during the compilation process, reducing boilerplate code and automating repetitive tasks.

Example:

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Text;
using System.Text;

[Generator]
public class SimpleClassGenerator : ISourceGenerator
{
    public void Initialize(GeneratorInitializationContext context)
    {
        // No initialization required for this example
    }

    public void Execute(GeneratorExecutionContext context)
    {
        var source = @"
            namespace GeneratedNamespace
            {
                public class GeneratedClass
                {
                    public string Property1 { get; set; }
                    public int Property2 { get; set; }
                }
            }";

        context.AddSource("GeneratedClass.g.cs", SourceText.From(source, Encoding.UTF8));
    }
}

In this example, the SimpleClassGenerator class implements the ISourceGenerator interface. The Execute method generates a new class named GeneratedClass with two properties and adds it to the compilation.

7. Create a gRPC service that performs CRUD operations on a data model.

gRPC is a high-performance framework for remote procedure calls. In .NET 6, creating a gRPC service involves defining the service and its methods in a .proto file, generating the server and client code, and implementing the service.

Example:

1. Define the .proto file:

syntax = "proto3";

option csharp_namespace = "GrpcService";

service DataService {
    rpc CreateData (DataRequest) returns (DataResponse);
    rpc ReadData (DataRequest) returns (DataResponse);
    rpc UpdateData (DataRequest) returns (DataResponse);
    rpc DeleteData (DataRequest) returns (DataResponse);
}

message DataRequest {
    int32 id = 1;
    string data = 2;
}

message DataResponse {
    string message = 1;
}

2. Implement the service in .NET 6:

public class DataService : DataService.DataServiceBase
{
    private readonly Dictionary<int, string> _dataStore = new();

    public override Task<DataResponse> CreateData(DataRequest request, ServerCallContext context)
    {
        _dataStore[request.Id] = request.Data;
        return Task.FromResult(new DataResponse { Message = "Data created successfully" });
    }

    public override Task<DataResponse> ReadData(DataRequest request, ServerCallContext context)
    {
        _dataStore.TryGetValue(request.Id, out var data);
        return Task.FromResult(new DataResponse { Message = data ?? "Data not found" });
    }

    public override Task<DataResponse> UpdateData(DataRequest request, ServerCallContext context)
    {
        if (_dataStore.ContainsKey(request.Id))
        {
            _dataStore[request.Id] = request.Data;
            return Task.FromResult(new DataResponse { Message = "Data updated successfully" });
        }
        return Task.FromResult(new DataResponse { Message = "Data not found" });
    }

    public override Task<DataResponse> DeleteData(DataRequest request, ServerCallContext context)
    {
        if (_dataStore.Remove(request.Id))
        {
            return Task.FromResult(new DataResponse { Message = "Data deleted successfully" });
        }
        return Task.FromResult(new DataResponse { Message = "Data not found" });
    }
}

8. Explain how configuration providers work and how they can be used in an application.

Configuration providers in .NET 6 load configuration settings from various sources into an application. These sources can include JSON files, environment variables, and command-line arguments.

Example:

using Microsoft.Extensions.Configuration;

var builder = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
    .AddEnvironmentVariables()
    .AddCommandLine(args);

IConfiguration configuration = builder.Build();

// Access configuration settings
var settingValue = configuration["MySettingKey"];

In this example, the configuration builder is set up to load configuration data from an appsettings.json file, environment variables, and command-line arguments.

9. Implement health checks for an ASP.NET Core application.

Health checks in an ASP.NET Core application monitor the health and status of the application and its dependencies. They provide a way to check if the application is running correctly and if its dependencies are available and functioning as expected.

Example:

// Add the required NuGet package
// dotnet add package Microsoft.AspNetCore.Diagnostics.HealthChecks

// In Program.cs
var builder = WebApplication.CreateBuilder(args);

// Add health checks services
builder.Services.AddHealthChecks()
    .AddCheck<ExampleHealthCheck>("example_health_check");

var app = builder.Build();

// Map health checks endpoint
app.MapHealthChecks("/health");

app.Run();

// Custom health check implementation
public class ExampleHealthCheck : IHealthCheck
{
    public Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
    {
        bool healthCheckResultHealthy = true; // Replace with actual health check logic

        if (healthCheckResultHealthy)
        {
            return Task.FromResult(HealthCheckResult.Healthy("The check indicates a healthy result."));
        }

        return Task.FromResult(HealthCheckResult.Unhealthy("The check indicates an unhealthy result."));
    }
}

10. Demonstrate how to implement authentication and authorization in an ASP.NET Core application.

Authentication and authorization in ASP.NET Core are implemented using middleware and attributes.

Example:

// Startup.cs
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication("CookieAuth")
            .AddCookie("CookieAuth", config =>
            {
                config.Cookie.Name = "UserLoginCookie";
                config.LoginPath = "/Home/Authenticate";
            });

        services.AddAuthorization(config =>
        {
            config.AddPolicy("Admin", policyBuilder => policyBuilder.RequireClaim("Admin"));
        });

        services.AddControllersWithViews();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseRouting();

        app.UseAuthentication();
        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}

// HomeController.cs
public class HomeController : Controller
{
    [Authorize]
    public IActionResult Secure()
    {
        return View();
    }

    [Authorize(Policy = "Admin")]
    public IActionResult AdminSecure()
    {
        return View();
    }

    public IActionResult Authenticate()
    {
        var claims = new List<Claim>
        {
            new Claim(ClaimTypes.Name, "User"),
            new Claim("Admin", "true")
        };

        var identity = new ClaimsIdentity(claims, "CookieAuth");
        var principal = new ClaimsPrincipal(identity);

        HttpContext.SignInAsync("CookieAuth", principal);

        return RedirectToAction("Index");
    }
}

11. Use EF Core migrations to add a new table to an existing database.

Entity Framework (EF) Core migrations manage database schema changes over time. They allow developers to define changes to the database schema in code, which can then be applied to the database.

Example:

// Step 1: Define the new table in your DbContext
public class ApplicationDbContext : DbContext
{
    public DbSet<NewTable> NewTables { get; set; }
}

public class NewTable
{
    public int Id { get; set; }
    public string Name { get; set; }
}

// Step 2: Create a new migration
// Run the following command in the Package Manager Console
// Add-Migration AddNewTable

// Step 3: Update the database
// Run the following command in the Package Manager Console
// Update-Database

12. Write unit tests for a service using xUnit.

Unit testing ensures that individual components of an application work as expected. In .NET 6, xUnit is a widely-used testing framework.

Example:

// Service to be tested
public class CalculatorService
{
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
}

// Unit tests using xUnit
public class CalculatorServiceTests
{
    private readonly CalculatorService _calculatorService;

    public CalculatorServiceTests()
    {
        _calculatorService = new CalculatorService();
    }

    [Fact]
    public void Add_ShouldReturnSumOfTwoNumbers()
    {
        // Arrange
        int a = 5;
        int b = 3;

        // Act
        int result = _calculatorService.Add(a, b);

        // Assert
        Assert.Equal(8, result);
    }

    [Fact]
    public void Subtract_ShouldReturnDifferenceOfTwoNumbers()
    {
        // Arrange
        int a = 5;
        int b = 3;

        // Act
        int result = _calculatorService.Subtract(a, b);

        // Assert
        Assert.Equal(2, result);
    }
}

In this example, the CalculatorService class has two methods: Add and Subtract. The CalculatorServiceTests class contains unit tests for these methods.

13. Explain the new minimal API feature in .NET 6 and its benefits.

Minimal APIs in .NET 6 provide a streamlined way to create HTTP APIs with minimal setup and configuration.

Example:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello, World!");

app.Run();

Benefits of Minimal APIs include reduced boilerplate, improved performance, ease of use, and flexibility.

14. Discuss the cross-platform capabilities of .NET 6.

.NET 6 is a cross-platform framework, allowing developers to build and run applications on multiple operating systems. It supports various architectures, making it suitable for a wide range of devices and environments. The framework provides consistent APIs and runtime behavior across different operating systems.

15. Discuss the impact of .NET 6’s performance improvements on application development.

.NET 6 has introduced several performance improvements, focusing on runtime optimizations, faster startup times, reduced memory usage, and improved throughput. Enhancements in the JIT compiler and garbage collection contribute to faster execution and smoother application performance. The framework libraries have also been optimized for performance, allowing applications to benefit from these improvements without code changes.