This article compiles essential ASP.NET Web API interview questions for experienced professionals. We'll cover a range of topics, from foundational concepts to advanced techniques, ensuring you're well-prepared for your next interview. We'll delve into both theoretical understanding and practical application, highlighting the key aspects recruiters look for in experienced candidates.
Foundational Knowledge:
1. What is ASP.NET Web API? How does it differ from ASP.NET MVC?
ASP.NET Web API is a framework for building HTTP services that can be accessed from various clients, including browsers, mobile devices, and other web services. Unlike ASP.NET MVC, which focuses on creating web applications with views and controllers for rendering HTML, Web API is specifically designed for building RESTful services that return data in formats like JSON or XML. The key difference lies in their purpose: MVC builds websites, while Web API builds APIs.
2. Explain RESTful principles and how they apply to ASP.NET Web API.
REST (Representational State Transfer) is an architectural style for building web services. Key principles include:
- Client-Server: The client and server are independent.
- Stateless: Each request from the client contains all the information needed to understand the request.
- Cacheable: Responses can be cached to improve performance.
- Uniform Interface: A consistent interface is used for all interactions.
- Layered System: The client doesn't need to know the underlying architecture.
- Code on Demand (Optional): The server can extend client functionality by sending executable code.
ASP.NET Web API facilitates the implementation of these principles through features like HTTP verbs (GET, POST, PUT, DELETE), routing, and content negotiation.
3. Describe different HTTP methods (GET, POST, PUT, DELETE) and their usage in Web API.
- GET: Retrieves data from the server. It's idempotent (multiple calls have the same effect as one).
- POST: Creates new data on the server. It's not idempotent.
- PUT: Updates existing data on the server. It's idempotent.
- DELETE: Deletes data from the server. It's idempotent.
Understanding the proper use of these methods is crucial for building RESTful services.
Intermediate to Advanced Concepts:
4. Explain different ways to handle exceptions in ASP.NET Web API.
Exception handling is crucial for building robust APIs. Methods include using try-catch blocks within controllers, creating custom exception filters (for global exception handling and custom responses), and leveraging exception logging tools for monitoring and debugging. A well-structured approach ensures graceful error handling and informative responses to clients.
5. How do you implement authentication and authorization in ASP.NET Web API?
ASP.NET Web API provides several ways to implement authentication and authorization:
- Basic Authentication: Simple, but insecure for sensitive data.
- OAuth 2.0: Industry-standard for secure authorization.
- JWT (JSON Web Tokens): Provides stateless authentication and authorization.
- Windows Authentication: Leverages Windows security.
Choosing the right mechanism depends on the security requirements of your API.
6. Discuss different ways to perform dependency injection in ASP.NET Web API.
Dependency injection is crucial for loose coupling, testability, and maintainability. Popular methods include:
- Constructor Injection: Dependencies are provided through the constructor.
- Property Injection: Dependencies are provided through properties.
- Method Injection: Dependencies are provided through method parameters.
Using a DI container like Unity, Autofac, or Ninject streamlines this process.
7. What are action filters and how are they used? Provide examples.
Action filters in ASP.NET Web API allow you to perform actions before or after an action method executes. Examples include:
- Authorization filters: Check if the user is authorized to access the resource.
- Exception filters: Handle exceptions that occur during the request.
- Action filters: Execute custom logic before and after the action method.
They enhance code modularity and maintainability.
8. Explain different approaches for handling asynchronous operations in Web API.
Asynchronous operations improve scalability and responsiveness. Techniques include:
- Using
asyncandawaitkeywords for asynchronous method calls. - Using Task-based asynchronous patterns.
These approaches help prevent blocking threads and optimize resource usage.
Advanced Topics & Best Practices:
9. How do you handle versioning in ASP.NET Web API?
Versioning your API is crucial to maintain compatibility with existing clients while adding new features. Approaches include:
- URI versioning: Include the version number in the URI (e.g.,
/api/v1/products). - Header versioning: Use a custom HTTP header to specify the version.
- Content negotiation: Use content negotiation to select the appropriate version based on the client's request.
Choosing the right approach depends on your needs and architectural preferences.
10. How do you optimize ASP.NET Web API for performance?
Optimizing performance involves several strategies, including:
- Caching: Cache frequently accessed data.
- Asynchronous programming: Avoid blocking threads.
- Efficient database queries: Optimize database interactions.
- Content negotiation: Serve appropriate content types.
- Profiling and monitoring: Identify and address performance bottlenecks.
This comprehensive list of ASP.NET Web API interview questions should provide a solid foundation for experienced professionals preparing for their next interview. Remember to thoroughly understand the underlying concepts and be prepared to discuss your practical experience with building and deploying Web APIs. Good luck!
