Tuesday, October 22, 2024

Part 2 - How to become Professional Programmer (Answers)

 Let's tackle these ASP.NET Core questions topic by topic:

1. ASP.NET Core Basics

Q1: What are the key differences between ASP.NET and ASP.NET Core?

  • Answer: ASP.NET Core is a cross-platform, high-performance framework, while ASP.NET (the older version) is Windows-only. ASP.NET Core is designed for cloud-based and internet-connected applications, with a modular and lightweight architecture. Key differences include:
    • Cross-platform support (Windows, macOS, Linux).
    • Built-in dependency injection.
    • Unified framework for MVC and Web API.
    • No longer depends on System.Web, resulting in better performance.

Q2: How does middleware work in the ASP.NET Core request pipeline?

  • Answer: Middleware components are assembled into a pipeline that handles HTTP requests. Each middleware component:
    1. Can handle an incoming request.
    2. Can decide whether to pass the request to the next middleware in the pipeline.
    3. Can perform operations after the downstream middleware has completed processing. Middleware is configured in Startup.cs via the Configure method.

Q3: What is the purpose of Startup.cs in an ASP.NET Core application?

  • Answer: Startup.cs is the entry point of an ASP.NET Core application and is responsible for:
    • Configuring services (via ConfigureServices method).
    • Configuring the HTTP request pipeline (via Configure method). It defines how the application behaves and responds to HTTP requests.

Q4: How can you configure dependency injection in ASP.NET Core?

  • Answer: Dependency injection is configured in the ConfigureServices method in Startup.cs. Services are added using AddSingleton, AddScoped, or AddTransient methods depending on the desired lifetime (singleton, scoped, transient). Example:
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services.AddScoped<IMyService, MyService>();

Q5: Explain the role of appsettings.json and how to read configuration values from it.

  • Answer: appsettings.json is a file used to store configuration settings in JSON format, including database connections, API keys, and environment-specific configurations. These settings can be accessed using the IConfiguration interface:
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public class MyClass {
    private readonly IConfiguration _config;
    public MyClass(IConfiguration config) {
        _config = config;
    }
    public void PrintConfigValue() {
        var myValue = _config["MyKey"];
    }
}

2. Routing and Endpoints

Q1: How does attribute routing differ from conventional routing in ASP.NET Core?

  • Answer: Attribute routing uses attributes on controller actions to define routes, while conventional routing is defined globally in the Startup.cs file. Attribute routing provides more control at the individual action level:
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[Route("products/{id}")]
public IActionResult GetProduct(int id) { }


Q2: How can you define custom route constraints in ASP.NET Core?

  • Answer: Custom route constraints can be defined using regular expressions or by implementing IRouteConstraint. Example using a regular expression:
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[Route("products/{id:regex(^\\d{{4}}$)}")]
public IActionResult GetProduct(int id) { }


Q3: What is endpoint routing, and how does it improve routing in ASP.NET Core 3.0+?

  • Answer: Endpoint routing decouples routing decisions from middleware execution. It improves performance by determining the endpoint before middleware is invoked, allowing middleware components to interact with the selected endpoint more efficiently.

Q4: How do you create and use route parameters in an MVC action method?

  • Answer: Route parameters can be used to capture values from the URL and pass them to the action method. For example:

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[Route("products/{id}")]
public IActionResult GetProduct(int id) {
    // id is captured from the route and passed as an argument
}


Q5: How can you handle route-specific errors in ASP.NET Core?

  • Answer: Route-specific errors can be handled using exception filters, middleware, or custom error pages. For example, use UseExceptionHandler middleware for global exception handling:
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app.UseExceptionHandler("/Home/Error");

3. Model Binding and Validation

Q1: How does ASP.NET Core bind form data to controller action parameters?

  • Answer: ASP.NET Core uses model binding to map form data (from query strings, route data, and form posts) to action method parameters. It binds data to simple types (int, string) and complex types (classes).

Q2: What are the different ways to perform input validation in ASP.NET Core?

  • Answer: Input validation can be performed using:
    • Data Annotations (e.g., [Required], [Range], [EmailAddress]).
    • FluentValidation (a more flexible validation library).
    • Custom validation attributes or logic in the controller.

Q3: How can you create custom validation attributes in ASP.NET Core?

  • Answer: Custom validation attributes can be created by inheriting from ValidationAttribute and overriding the IsValid method:
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public class CustomEmailAttribute : ValidationAttribute {
    protected override bool IsValid(object value) {
        var email = value as string;
        return email != null && email.EndsWith("@example.com");
    }
}

Q4: Explain how you would use FluentValidation in an ASP.NET Core project.

  • Answer: FluentValidation is used to create validation logic in a more fluent and customizable way. Install the FluentValidation.AspNetCore package, and create a validator:
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public class ProductValidator : AbstractValidator<Product> {
    public ProductValidator() {
        RuleFor(p => p.Name).NotEmpty().WithMessage("Name is required.");
    }
}

Q5: How does model binding handle complex objects and collections?

  • Answer: ASP.NET Core can bind complex objects and collections by recursively binding properties. For example:
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public IActionResult CreateOrder(Order order) {
    // ASP.NET Core binds nested objects like Order.Customer automatically
}


4. Dependency Injection (DI)

Q1: What are the different service lifetimes (Scoped, Transient, Singleton) in ASP.NET Core DI?

  • Answer:
    • Singleton: The service is created once and shared across the entire application lifetime.
    • Scoped: The service is created once per request (or scope) and shared within that request.
    • Transient: A new instance of the service is created every time it is requested.

Q2: How would you inject a service into a middleware?

  • Answer: To inject a service into middleware, use constructor injection or the Invoke method. The service must be registered in Startup.cs. Example:
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public class MyMiddleware {
    private readonly RequestDelegate _next;
    private readonly IMyService _myService;
    public MyMiddleware(RequestDelegate next, IMyService myService) {
        _next = next;
        _myService = myService;
    }
    public async Task Invoke(HttpContext context) {
        // Use the service
        await _next(context);
    }
}

Q3: Explain how you can implement multiple constructors in a class using DI.

  • Answer: ASP.NET Core's DI system selects the constructor with the most parameters that it can resolve. If you have multiple constructors, ensure that at least one of them has all dependencies resolvable by DI. You can manually select a constructor by modifying the service registration.

Q4: How do you handle circular dependencies in ASP.NET Core DI?

  • Answer: Circular dependencies occur when two or more services depend on each other, leading to a deadlock. You can resolve this by:
    • Refactoring the code to remove circular dependencies.
    • Using lazy loading (Lazy<T> or Func<T>) to delay instantiation.

Q5: What is the benefit of using IServiceProvider in ASP.NET Core?

  • Answer: IServiceProvider is used to resolve services manually, typically in scenarios where DI isn't automatically handled (e.g., within middleware). It allows dynamic resolution of dependencies at runtime.

5. Middleware

Q1: How can you create a custom middleware component in ASP.NET Core?

  • Answer: Custom middleware can be created by implementing a class with an Invoke or InvokeAsync method, and registering it in the Startup.cs file. Example:

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public class MyCustomMiddleware {
    private readonly RequestDelegate _next;
    public MyCustomMiddleware(RequestDelegate next) {
        _next = next;
    }
    public async Task Invoke(HttpContext context) {
        // Middleware logic here
        await _next(context);
    }
}

Q2: Explain the order of middleware execution in the ASP.NET Core pipeline.

  • Answer: Middleware components execute in the order they are registered in the Startup.Configure method. Each middleware can either:
    • Handle the request and prevent further processing.
    • Pass the request to the next middleware by calling _next(context).

Q3: What are the benefits of using the built-in UseExceptionHandler middleware?

  • Answer: UseExceptionHandler allows centralized handling of exceptions in ASP.NET Core. It ensures that any unhandled exceptions are caught and can be logged or redirected to a custom error page, improving user experience and simplifying error management.

Q4: How does the Run, Use, and Map methods differ in middleware configuration?

  • Answer:
    • Use: Registers a middleware and passes control to the next component in the pipeline.
    • Run: Registers a terminal middleware, meaning it handles the request and doesn’t call the next middleware.
    • Map: Branches the middleware pipeline based on the request path.

Q5: How would you implement middleware to handle request logging?

  • Answer: Create custom middleware to log request details (e.g., URL, headers) and register it in the pipeline:

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public async Task Invoke(HttpContext context) {
    var request = context.Request;
    Console.WriteLine($"Request URL: {request.Path}");
    await _next(context);  // Call the next middleware
}

Part 1 - How to become Professional Programmer (Questions)

 To become an expert in ASP.NET Core, you need to cover a wide range of topics. Below are 15 key topics, each accompanied by 5 challenging questions to test your knowledge and deepen your understanding:


1. ASP.NET Core Basics

  1. What are the key differences between ASP.NET and ASP.NET Core?
  2. How does middleware work in the ASP.NET Core request pipeline?
  3. What is the purpose of Startup.cs in an ASP.NET Core application?
  4. How can you configure dependency injection in ASP.NET Core?
  5. Explain the role of appsettings.json and how to read configuration values from it.

2. Routing and Endpoints

  1. How does attribute routing differ from conventional routing in ASP.NET Core?
  2. How can you define custom route constraints in ASP.NET Core?
  3. What is endpoint routing, and how does it improve routing in ASP.NET Core 3.0+?
  4. How do you create and use route parameters in an MVC action method?
  5. How can you handle route-specific errors in ASP.NET Core?

3. Model Binding and Validation

  1. How does ASP.NET Core bind form data to controller action parameters?
  2. What are the different ways to perform input validation in ASP.NET Core?
  3. How can you create custom validation attributes in ASP.NET Core?
  4. Explain how you would use FluentValidation in an ASP.NET Core project.
  5. How does model binding handle complex objects and collections?

4. Dependency Injection (DI)

  1. What are the different service lifetimes (Scoped, Transient, Singleton) in ASP.NET Core DI?
  2. How would you inject a service into a middleware?
  3. Explain how you can implement multiple constructors in a class using DI.
  4. How do you handle circular dependencies in ASP.NET Core DI?
  5. What is the benefit of using IServiceProvider in ASP.NET Core?

5. Middleware

  1. How can you create a custom middleware component in ASP.NET Core?
  2. Explain the order of middleware execution in the ASP.NET Core pipeline.
  3. What are the benefits of using the built-in UseExceptionHandler middleware?
  4. How does the Run, Use, and Map methods differ in middleware configuration?
  5. How would you implement middleware to handle request logging?

6. Authentication and Authorization

  1. How does the authentication middleware work in ASP.NET Core?
  2. What are policies in ASP.NET Core Authorization, and how do they work?
  3. How can you implement JWT-based authentication in ASP.NET Core?
  4. How do role-based and claims-based authorization differ in ASP.NET Core?
  5. How do you secure specific controller actions with custom authorization logic?

7. Entity Framework Core

  1. How would you configure a DbContext in ASP.NET Core?
  2. What is the difference between DbContext.SaveChanges() and DbContext.SaveChangesAsync()?
  3. How do you handle database migrations in Entity Framework Core?
  4. Explain the role of LINQ in querying databases with Entity Framework Core.
  5. What strategies are available for handling concurrency in Entity Framework Core?

8. Logging and Monitoring

  1. How do you implement structured logging in ASP.NET Core?
  2. What is the purpose of ILogger<T>, and how do you use it in a controller or service?
  3. How can you integrate third-party logging providers (e.g., Serilog, NLog) in ASP.NET Core?
  4. How can you configure and manage log levels in ASP.NET Core?
  5. What are the key benefits of using Application Insights for monitoring in an ASP.NET Core app?

9. Web API Development

  1. What is the difference between Controller and ControllerBase in ASP.NET Core Web API?
  2. How would you implement versioning in an ASP.NET Core Web API?
  3. Explain how to handle content negotiation in an ASP.NET Core Web API.
  4. How can you implement custom exception handling in an ASP.NET Core Web API?
  5. What is HATEOAS, and how do you implement it in an ASP.NET Core Web API?

10. Performance Optimization

  1. How do you implement response caching in ASP.NET Core?
  2. What strategies can you use to minimize memory usage in an ASP.NET Core app?
  3. How do you optimize database queries in ASP.NET Core applications?
  4. Explain the purpose of Output Caching in ASP.NET Core.
  5. How would you configure and use a distributed cache (e.g., Redis) in ASP.NET Core?

11. Security

  1. How can you prevent Cross-Site Request Forgery (CSRF) in ASP.NET Core?
  2. What is HTTPS redirection, and how can you enforce HTTPS in an ASP.NET Core app?
  3. How do you handle and mitigate Cross-Site Scripting (XSS) attacks in ASP.NET Core?
  4. Explain how data protection APIs work in ASP.NET Core.
  5. What strategies can you use to secure sensitive data such as connection strings?

12. Real-Time Communication with SignalR

  1. What is SignalR, and how does it enable real-time communication in ASP.NET Core?
  2. How do SignalR hubs work, and how do clients interact with them?
  3. Explain the different transport methods used by SignalR.
  4. How can you scale out a SignalR application using Azure SignalR Service?
  5. How do you manage client connections and groups in SignalR?

13. Azure Integration

  1. How do you deploy an ASP.NET Core app to Azure App Service?
  2. What are the key features of Azure Key Vault, and how do you use it to store secrets in an ASP.NET Core app?
  3. How do you configure an ASP.NET Core app to use Azure SQL Database?
  4. How do you implement Azure AD authentication in an ASP.NET Core application?
  5. Explain how you can use Azure App Configuration in ASP.NET Core for dynamic configuration.

14. Testing and Debugging

  1. How do you implement unit testing for controllers in ASP.NET Core?
  2. What is integration testing, and how would you perform it in an ASP.NET Core app?
  3. How can you test middleware components in ASP.NET Core?
  4. Explain how you would use Mock objects in unit tests.
  5. What are the key tools for debugging and performance analysis in ASP.NET Core?

15. Globalization and Localization

  1. How do you configure localization and culture settings in ASP.NET Core?
  2. Explain the difference between resource-based and database-based localization.
  3. How can you dynamically change the language or culture in an ASP.NET Core app?
  4. How do you handle localized data validation in ASP.NET Core?
  5. How can you use different localization strategies (e.g., browser-based, query string-based) in your application?

By mastering these topics and being able to answer the corresponding questions, you'll be well on your way to becoming an expert in ASP.NET Core.

Go to Part 2 for Answers

Ten Projects Ideas for learning C# and ASP.NET

 Here's a list of 10 practical coding tasks that are moderately challenging, allowing you to test different aspects of your skills in ASP.NET Core, Azure, and related technologies:

1. Blogging Platform with Authentication

  • Tech Stack: ASP.NET Core, Entity Framework Core, Identity
  • Task: Build a blogging platform where users can register, create, edit, and delete posts. Implement user roles (admin, editor, reader) with varying permissions.
  • Focus: Authentication, role management, and CRUD operations.


2. Task Management System with Notification

  • Tech Stack: ASP.NET Core, SignalR, SQL Server
  • Task: Develop a task management system for a small team. Each user can assign tasks to others, set deadlines, and mark them as complete. Include real-time notifications using SignalR.
  • Focus: Real-time communication, task scheduling, and data persistence.


3. File Upload Portal with Azure Blob Storage

  • Tech Stack: ASP.NET Core, Azure Blob Storage
  • Task: Create a web app where users can upload large files (like videos) and store them in Azure Blob Storage. Include file versioning and metadata tracking.
  • Focus: File upload, Azure integration, and scalability.


4. E-Commerce Mini-Store

  • Tech Stack: ASP.NET Core, Stripe/PayPal API, Entity Framework Core
  • Task: Build a small e-commerce store that includes product browsing, adding to a cart, and payment processing with Stripe or PayPal. Implement basic order management.
  • Focus: API integration, payment processing, and transaction handling.


5. Social Media Aggregator

  • Tech Stack: ASP.NET Core, REST APIs (e.g., Twitter, Facebook)
  • Task: Create a dashboard that aggregates posts from various social media platforms. Users can add/remove accounts and view posts in a unified timeline.
  • Focus: API consumption, OAuth, and asynchronous data fetching.


6. Quiz Application with Timed Challenges

  • Tech Stack: ASP.NET Core, Entity Framework Core, jQuery
  • Task: Build a quiz application where users can take timed quizzes on different subjects. Add multiple-choice and fill-in-the-blank questions, and generate scores dynamically.
  • Focus: Front-end interaction, time management, and scoring logic.


7. Event Booking System with Calendar Integration

  • Tech Stack: ASP.NET Core, Google Calendar API, SQL Server
  • Task: Create an event booking system where users can reserve seats for events. Include calendar integration so users can sync their reservations with Google Calendar.
  • Focus: API integration, event scheduling, and calendar functionality.


8. Azure Function-based Microservice

  • Tech Stack: Azure Functions, ASP.NET Core
  • Task: Develop a set of microservices using Azure Functions. These microservices should handle different tasks (e.g., processing orders, sending emails) and interact with an ASP.NET Core app.
  • Focus: Serverless architecture, Azure Functions, and distributed systems.


9. Custom URL Shortener

  • Tech Stack: ASP.NET Core, Entity Framework Core
  • Task: Build a URL shortener service, where users can create shortened URLs for long ones. Track usage statistics like click counts and user locations.
  • Focus: URL rewriting, data tracking, and statistics reporting.


10. Job Search Aggregator

  • Tech Stack: ASP.NET Core, REST APIs (LinkedIn, Indeed, etc.)
  • Task: Create an aggregator for job listings from multiple platforms. Users can search and filter jobs by location, role, and other parameters.
  • Focus: API integration, search/filter functionality, and front-end optimization.


These tasks are challenging but achievable within a few days or a week, depending on your focus. They will test different areas of your knowledge in ASP.NET Core, API integration, Azure, real-time systems, and database management.

Tuesday, October 15, 2024

Part 2 - Using Unit Tests in ASP.NET Core Application (Simple)

Unit testing in ASP.NET Core is a key aspect of writing maintainable and testable applications. In this tutorial, I'll walk you through creating a simple unit test in an ASP.NET Core application using the xUnit framework.

Prerequisites

  • .NET Core SDK installed
  • Visual Studio or any preferred IDE
  • xUnit framework

Step 1: Set Up Your ASP.NET Core Project

Create a new ASP.NET Core web application:

  1. Open Visual Studio.
  2. Select Create a new project.
  3. Choose ASP.NET Core Web Application and click Next.
  4. Name the project (e.g., SampleApp).
  5. Select ASP.NET Core Empty or MVC template depending on your needs.

Step 2: Install the xUnit Testing Framework

You need to add xUnit and xUnit Runner to your test project. In Visual Studio, right-click on the solution and:

  1. Select Add > New Project.
  2. Choose xUnit Test Project and click Next.
  3. Name the project (e.g., SampleApp.Tests) and click Create.

Once the test project is created, install any additional dependencies:

  1. Open NuGet Package Manager (right-click your SampleApp.Tests project).
  2. Search and install:
    • xUnit
    • xUnit.runner.visualstudio
    • Moq (optional, for mocking objects).

Step 3: Writing a Simple Unit Test

Let's say you have a simple service in your application that calculates tax:

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// TaxService.cs in SampleApp
public class TaxService
{
    public decimal CalculateTax(decimal amount, decimal rate)
    {
        return amount * rate;
    }
}

Unit Test for TaxService

In the test project, create a test class for this service:

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// TaxServiceTests.cs in SampleApp.Tests
using Xunit;

public class TaxServiceTests
{
    [Fact]
    public void CalculateTax_ValidAmountAndRate_ReturnsCorrectTax()
    {
        // Arrange
        var taxService = new TaxService();
        decimal amount = 100m;
        decimal rate = 0.1m; // 10%

        // Act
        var result = taxService.CalculateTax(amount, rate);

        // Assert
        Assert.Equal(10m, result);
    }
}


Explanation:

  • [Fact]: This attribute marks the method as a test case in xUnit.
  • Arrange: Set up the test data and service.
  • Act: Call the method under test.
  • Assert: Verify that the method’s result is as expected.

Step 4: Run the Tests

To run the tests:

  1. Go to Test > Test Explorer in Visual Studio.
  2. Build the solution.
  3. The Test Explorer window should list your test. Click Run All to execute the tests.

If everything is set up correctly, your test should pass, and you'll see a green checkmark next to the test.

Step 5: Expanding Tests

You can add more tests to handle edge cases. For example, what happens when the rate is 0 or the amount is negative?

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[Fact]
public void CalculateTax_ZeroRate_ReturnsZero()
{
    var taxService = new TaxService();
    var result = taxService.CalculateTax(100m, 0m);
    Assert.Equal(0m, result);
}

[Fact]
public void CalculateTax_NegativeAmount_ReturnsNegativeTax()
{
    var taxService = new TaxService();
    var result = taxService.CalculateTax(-100m, 0.1m);
    Assert.Equal(-10m, result);
}


Step 6: Mocking Dependencies (Optional)

If your service has dependencies, you can use Moq to mock those. For example, if the TaxService depends on an ILogger, you can mock it:

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using Moq;
using Microsoft.Extensions.Logging;

[Fact]
public void CalculateTax_UsesLogger()
{
    var loggerMock = new Mock<ILogger<TaxService>>();
    var taxService = new TaxService(loggerMock.Object);
    var result = taxService.CalculateTax(100m, 0.1m);

    // Verify logger was used
    loggerMock.Verify(logger => logger.Log(
        It.IsAny<LogLevel>(),
        It.IsAny<EventId>(),
        It.IsAny<object>(),
        It.IsAny<Exception>(),
        It.IsAny<Func<object, Exception, string>>()
    ));
}

Part 1 - Unit Testing In ASP.NET Core

Introduction to Unit Testing

Unit testing is used to validate that individual components of your software (usually functions or methods) work as expected. 

Purpose of Unit Testing

Here are some key benefits:

  1. Verify correctness: Unit tests ensure that the smallest units of code behave as intended, catching bugs early.
  2. Improve code quality: Well-tested code is often cleaner and easier to maintain, as unit testing encourages developers to write more modular and clear code.
  3. Facilitate refactoring: With a solid suite of unit tests, you can refactor code confidently, knowing the tests will catch any unintended changes or breakages.
  4. Ensure reliability: Automated unit tests help reduce the chance of regression, where a new change inadvertently breaks existing functionality.
  5. Enable faster development: Once set up, unit tests can be run automatically, speeding up development by reducing the need for manual testing.

In essence, unit testing helps maintain a stable and reliable codebase, making it easier to catch issues early in the development process.

Type of Unit Testing in ASP.NET and Desktop Application In Visual Studio

  • xUnit
  • NUnit

Philosophy and Design

  • xUnit:
    • xUnit is designed with simplicity and extensibility in mind. It enforces best practices by avoiding static test methods and encourages writing isolated, easily testable code.
    • Test methods are usually instance methods, meaning a new instance of the test class is created for each test case. This encourages better isolation between tests.
  • NUnit:
    • NUnit has a more traditional approach to unit testing. It allows both static and instance test methods, which gives flexibility but can sometimes lead to less isolated tests.
    • It is older than xUnit and has a rich set of features built over time.