Mastering .NET Core and Web API Interview Questions: Top 20 Q&A for Success

Introduction:

Welcome to our comprehensive guide on mastering .NET Core and Web API interview questions! In this article, we will empower you with the essential knowledge and insights needed to excel in your .NET Core and Web API interviews. By familiarizing yourself with these top 20 interview questions and their expert answers, you’ll gain the confidence and expertise necessary to stand out among other candidates. Let’s embark on this journey together and unlock the secrets to interview success!

.NET Core and Web API Interview Questions

1. What is .NET Core? How is it different from the traditional .NET Framework?
   • .NET Core is an open-source, cross-platform framework for building modern applications. It is different from the traditional .NET Framework in that it is modular, lightweight, and optimized for performance. It can run on Windows, macOS, and Linux.
2. Explain the concept of Dependency Injection in .NET Core. How does it help with application development?
   • Dependency Injection (DI) is a design pattern used in .NET Core to provide loose coupling and better testability. It allows you to inject dependencies into a class rather than having the class create them itself. DI helps improve modularity, maintainability, and scalability of the application.
3. What are the differences between the three service lifetimes in dependency injection: AddScoped, AddSingleton, and AddTransient?
   • AddScoped: A new instance is created for each scope (e.g., each HTTP request). The same instance is shared within the scope but different across scopes.
   • AddSingleton: Only one instance is created throughout the application lifetime. The same instance is shared across all requests.
   • AddTransient: A new instance is created each time the dependency is requested. No instance sharing occurs.
4. What is ASP.NET Core Web API? How does it differ from MVC?
   • ASP.NET Core Web API is a framework for building HTTP-based APIs. It is designed specifically for building RESTful services that can be consumed by various clients. It differs from MVC (Model-View-Controller) in that it focuses on handling HTTP requests and returning data in various formats (such as JSON or XML) instead of generating HTML views.
5. Explain the concept of Middleware in ASP.NET Core. How is it used in request processing?
   • Middleware in ASP.NET Core is software components that are responsible for handling requests and responses in the application pipeline. Each middleware component can inspect, modify, or terminate the request/response. Middleware components are executed in a specific order, allowing developers to customize the request processing pipeline.
6. What are the common HTTP verbs used in Web API development? Explain their purposes.
   • GET: Retrieves data from the server.
   • POST: Submits data to the server to create a new resource.
   • PUT: Updates an existing resource on the server.
   • DELETE: Deletes a resource on the server.
   • PATCH: Partially updates a resource on the server.
7. How do you handle authentication and authorization in ASP.NET Core Web API?
   • ASP.NET Core Web API provides built-in authentication and authorization middleware. You can configure various authentication schemes like JWT, OAuth, or cookies. Authorization can be done using attributes, policies, or custom authorization handlers.
8. Explain the concept of Model Binding in ASP.NET Core Web API. How does it work?
   • Model Binding is a process in ASP.NET Core Web API that maps incoming HTTP request data to action method parameters or model classes. It automatically converts query string, form data, and route values into strongly typed objects.
9. What are the different types of response formats supported by Web API? How do you return JSON or XML responses?
   • Web API supports multiple response formats such as JSON, XML, and others. By default, JSON is the most commonly used format. To return JSON or XML responses, you can use the ContentNegotiation feature to configure the desired format based on client requests or use the Produces attribute on action methods.
10. Can you explain how CORS (Cross-Origin Resource Sharing) works in ASP.NET Core Web API?
    • CORS (Cross-Origin Resource Sharing) is a security mechanism that allows web browsers to make cross-origin requests from one domain to another. In ASP.NET Core Web API, CORS can be enabled by configuring the CORS middleware. It adds appropriate headers to the API responses, allowing the browser to determine if the client-side JavaScript code is allowed to access the requested resources. CORS can be configured to specify the allowed origins, HTTP methods, headers, and other settings to control and secure cross-origin requests.
11. Explain the concept of Middleware Pipeline in ASP.NET Core. How does the request flow through the pipeline?
    • The Middleware Pipeline in ASP.NET Core is a sequence of components called Middleware. Each Middleware component can handle an aspect of the HTTP request/response pipeline. The request flows through the pipeline from top to bottom, and each Middleware component can modify the request or response before passing it to the next component. The final Middleware component generates the response and sends it back to the client.
12. What is the purpose of IActionResult in ASP.NET Core Web API? How do you return different types of responses using IActionResult?
    • IActionResult is an interface in ASP.NET Core that represents an action result. It allows you to return different types of HTTP responses from action methods. You can return various implementations of IActionResult, such as OkResult, NotFoundResult, JsonResult, and others, based on the desired response type. Each implementation represents a specific HTTP status code and response format.
13. What are the different types of routing available in ASP.NET Core Web API? Explain their differences and use cases.
    • In ASP.NET Core Web API, there are two types of routing available: convention-based routing and attribute routing. Convention-based routing uses route templates based on conventions to map incoming requests to action methods. Attribute routing, on the other hand, uses attributes directly applied to the action methods or controllers to define the route templates. Attribute routing provides more flexibility and control over the routing configuration, making it suitable for complex scenarios or when you want to define explicit routes.
14. How do you handle exceptions in ASP.NET Core Web API? Explain the use of exception filters and global exception handling.
    • In ASP.NET Core Web API, exceptions can be handled using exception filters and global exception handling. Exception filters are attributes that can be applied to action methods or controllers to handle specific exceptions. They allow you to customize the response or perform additional actions when an exception occurs. Global exception handling, on the other hand, involves configuring a global exception handler in the application’s Startup class. It catches unhandled exceptions that occur during the request processing and allows you to log or format the error response consistently.
15. What is the purpose of the HttpClient class in .NET Core? How do you consume external APIs in your Web API project?
    • The HttpClient class in .NET Core is a powerful class that allows you to send HTTP requests and receive HTTP responses from external APIs. It provides methods to make various types of requests (GET, POST, PUT, DELETE, etc.) and handle the responses. In a Web API project, you can use the HttpClient class to consume external APIs by creating an instance of HttpClient, making the necessary requests, and processing the received responses.
16. Explain the concept of versioning in Web API. How do you handle versioning of your API endpoints?
    • Versioning in Web API refers to maintaining multiple versions of API endpoints to handle different client requirements or changes in the API’s behavior over time. In ASP.NET Core Web API, versioning can be implemented using either URL-based versioning, query string-based versioning, or header-based versioning. Each approach has its own conventions and advantages. It allows you to introduce breaking changes or add new features to the API without affecting existing clients.
17. How do you implement caching in ASP.NET Core Web API? Explain the use of in-memory cache and distributed cache.
    • Caching in ASP.NET Core Web API can be implemented using two cache providers: in-memory cache and distributed cache.
    • In-memory cache is a simple cache provider that stores data in the application’s memory. It is suitable for scenarios where the cached data is not shared across multiple instances or when the cache size is limited to the available memory.
    • Distributed cache, on the other hand, allows you to store cached data in a distributed cache store, such as Redis or SQL Server. It enables sharing the cache data across multiple instances or even multiple applications running on different servers. This is useful in load-balanced or cloud-based scenarios.
18. What is the purpose of the IActionResult interface in ASP.NET Core Web API? How is it used in action methods?
    • The IActionResult interface in ASP.NET Core Web API represents the result of an action method. It allows you to return different types of HTTP responses from your action methods.
    • By returning an IActionResult from an action method, you can customize the HTTP status code, response body, and other properties of the response. It provides flexibility in handling different scenarios, such as returning a specific status code (e.g., 200 OK or 404 Not Found), returning JSON or XML data, or redirecting to another URL.
19. Explain the concept of content negotiation in ASP.NET Core Web API. How do you support multiple response formats?
    • Content negotiation in ASP.NET Core Web API refers to the process of selecting the appropriate response format (e.g., JSON, XML) based on the client’s preferences or the request’s Accept header.
    • ASP.NET Core Web API automatically performs content negotiation by examining the request’s Accept header and the configured response formatters. It selects the formatter that best matches the client’s preferences or the default formatter if no match is found.
    • To support multiple response formats, you can configure additional formatters, such as JSON and XML formatters, in the application’s Startup class. The client can then specify their preferred format using the Accept header, and the API will respond accordingly.
20. How do you secure your ASP.NET Core Web API using JWT (JSON Web Tokens) authentication? Explain the authentication flow and token validation process.
    • JWT authentication is a popular method to secure ASP.NET Core Web APIs. The authentication flow involves the following steps:
      • The client sends a request to the API with the JWT token included in the Authorization header.
      • The API extracts the token from the header and validates it.
      • The token validation process includes verifying the signature, expiration, and issuer of the token, as well as checking any custom claims or roles.
      • If the token is valid, the API grants access to the requested resource.
      • If the token is invalid or expired, the API returns a 401 Unauthorized response.
    • To implement JWT authentication in ASP.NET Core, you need to configure the authentication middleware in the Startup class, specifying the token validation parameters, issuer, audience, and secret key.
    • Additionally, you can use frameworks like IdentityServer4 or Microsoft.AspNetCore.Authentication.JwtBearer to simplify the token validation and authentication process.

Conclusion:

Congratulations! You have now acquired a deep understanding of the most crucial .NET Core and Web API interview questions. With this knowledge, you have armed yourself to tackle challenging interviews and demonstrate your proficiency in these technologies. Remember to apply the insights gained from this guide by practicing your responses, reinforcing your understanding of key concepts, and staying updated with the latest advancements in the .NET Core and Web API ecosystems. With your newfound expertise, go out there and confidently pursue your dream job or professional growth. Best of luck on your journey to becoming a .NET Core and Web API master!