Web API Interview Questions & Answers

Basics of Web API:

1. What is Web API?

   • Answer: Web API (Application Programming Interface) is a framework for building HTTP services that can be consumed by a broad range of clients, including browsers, mobile devices, and desktop applications.

2. Differentiate between Web API and WCF.

   • Answer: Web API is a framework for building HTTP services, primarily RESTful, while WCF (Windows Communication Foundation) is a broader framework for building various types of services, including RESTful, SOAP, and more.

3. Explain REST and its principles.

   • Answer: REST (Representational State Transfer) is an architectural style for designing networked applications. Its principles include statelessness, client-server architecture, and resource-based interactions.

4. What is the purpose of the WebApiConfig class in Web API?

   • Answer: The WebApiConfig class is used to configure routes, formatters, and other settings for Web API within an ASP.NET application.

5. What is the significance of HTTP in Web API?

   • Answer: HTTP (Hypertext Transfer Protocol) is the foundation of communication in Web API. It defines methods like GET, POST, PUT, DELETE, etc., and status codes for communication between clients and servers.

Routing in Web API:

6. Explain the concept of routing in Web API.

   • Answer: Routing in Web API maps incoming HTTP requests to the appropriate action methods based on the URL pattern defined in the route configuration.

7. How can you enable attribute-based routing in Web API?

   • Answer: Attribute-based routing is enabled by adding the [Route] attribute to the controller or action method in Web API.

8. Differentiate between conventional routing and attribute routing.

   • Answer: Conventional routing is configured in the route table, while attribute routing is defined using attributes directly on the controller and action methods.

HTTP Methods and Status Codes:

9. Explain the purpose of the HTTP GET method in Web API.

   • Answer: The HTTP GET method is used to retrieve data from a specified resource in Web API.

10. What is the role of the HTTP POST method?

    • Answer: The HTTP POST method is used to submit data to be processed to a specified resource in Web API.

11. When should you use HTTP PUT in Web API?

    • Answer: HTTP PUT is used to update a resource or create a new resource if it does not exist at a specified URL.

12. Explain the significance of HTTP DELETE in Web API.

    • Answer: HTTP DELETE is used to request the removal of a resource identified by a specific URL.

13. What are HTTP status codes? Provide examples.

    • Answer: HTTP status codes indicate the success or failure of an HTTP request. Examples include 200 OK (success), 404 Not Found (resource not found), and 500 Internal Server Error (server error).

Content Negotiation:

14. What is content negotiation in Web API?

    • Answer: Content negotiation is the process of selecting the appropriate response format (JSON, XML, etc.) based on the client's request.

15. How does Web API support content negotiation?

    • Answer: Web API supports content negotiation through the use of media formatters, which are responsible for serializing and deserializing data in different formats.

Model Binding and Validation:

16. Explain model binding in Web API.

    • Answer: Model binding is the process of mapping data from HTTP requests to parameters of a Web API action method.

17. What is model validation in Web API?

    • Answer: Model validation ensures that the data received from the client conforms to the expected format and constraints defined by the model.

18. How can you perform model validation in Web API?

    • Answer: Model validation is performed automatically by Web API based on data annotations on model properties and can be triggered using ModelState.IsValid in the controller.

Filters and Middleware:

19. What are filters in Web API?

    • Answer: Filters are attributes or classes that can be applied to controllers and actions to modify the request or response processing pipeline.

20. Explain the use of the [Authorize] attribute in Web API.

    • Answer: The [Authorize] attribute restricts access to a controller or action to authenticated users.

21. What is middleware in the context of Web API?

    • Answer: Middleware in Web API refers to components that participate in the request/response processing pipeline. Examples include authentication middleware and exception handling middleware.

Security in Web API:

22. How can you secure a Web API?

    • Answer: Web API security can be implemented using various mechanisms such as API keys, OAuth, and JWT (JSON Web Tokens).

23. Explain the role of CORS in Web API security.

    • Answer: Cross-Origin Resource Sharing (CORS) is a security feature that controls which domains can access resources on a server. It prevents unauthorized access from different domains.

Exception Handling:

24. How do you handle exceptions in Web API?

    • Answer: Exceptions in Web API can be handled using try-catch blocks in the controller, global exception filters, or custom exception handling middleware.

25. Explain the purpose of IHttpActionResult.

    • Answer: IHttpActionResult is an interface in Web API that represents an HTTP response. It provides a standardized way to create HTTP responses within action methods.

Versioning in Web API:

26. Why is API versioning important, and how can it be achieved in Web API?

    • Answer: API versioning is important for maintaining backward compatibility. Versioning in Web API can be achieved through URI versioning, query string versioning, or header versioning.

27. What is URI versioning in Web API?

    • Answer: URI versioning involves including the version number in the API's URL, such as "/api/v1/products."

Dependency Injection:

28. How does dependency injection work in Web API?

    • Answer: Dependency injection in Web API involves injecting dependencies, such as services or repositories, into controllers or other components to promote loose coupling.

29. Explain the use of the [FromUri] and [FromBody] attributes.

    • Answer: [FromUri] is used to bind parameters from the URI, while [FromBody] is used to bind parameters from the request body in Web API.

Testing Web API:

30. How can you test Web API methods?

    • Answer: Web API methods can be tested using tools like Postman, Swagger, or by writing unit tests using testing frameworks like NUnit or xUnit.

31. Explain the purpose of the IHttpActionResult interface in testing.

    • Answer: IHttpActionResult simplifies the testing of Web API methods by providing a standardized way to create HTTP responses, making it easier to assert expected results.

RESTful Best Practices:

32. What are some best practices for designing RESTful Web APIs?
    • Answer: Best practices include using meaningful resource URIs, leveraging HTTP methods appropriately, using proper status codes, and supporting content

negotiation.

33. Explain HATEOAS and its role in RESTful APIs.
    • Answer: HATEOAS (Hypermedia as the Engine of Application State) involves including hypermedia links in the API responses, allowing clients to navigate the API dynamically.

Serialization and Deserialization:

34. What is serialization, and how is it used in Web API?

    • Answer: Serialization is the process of converting an object into a format suitable for transport, such as JSON or XML. Web API uses serialization to send data in response to client requests.

35. How does Web API handle object serialization and deserialization?

    • Answer: Web API uses media formatters for serialization and deserialization. JSON and XML formatters are included by default.

Caching in Web API:

36. Explain caching in Web API.

    • Answer: Caching in Web API involves storing and reusing responses to improve performance. It can be implemented using HTTP caching headers.

37. What are ETags, and how are they used in caching?

    • Answer: ETags (Entity Tags) are identifiers assigned to resources. They are used in caching to check if a resource has been modified since it was last requested.

Streaming in Web API:

38. How can you implement streaming in Web API?
    • Answer: Streaming in Web API can be implemented using the HttpResponseMessage class and streaming large files or data directly to the response stream.

Middleware in Web API:

39. Explain the concept of middleware in ASP.NET Core Web API.

    • Answer: Middleware in ASP.NET Core Web API is a pipeline of components that handle requests and responses. Each middleware component processes the request and can modify the response.

40. What is the purpose of the UseExceptionHandler middleware in Web API?

    • Answer: UseExceptionHandler middleware is used to catch unhandled exceptions and return a custom error response in Web API.

OAuth and JWT:

41. How does OAuth work in Web API security?

    • Answer: OAuth is an authorization framework that allows third-party applications to access resources on behalf of the resource owner. It is commonly used for securing Web API endpoints.

42. What is JWT, and how is it used in Web API authentication?

    • Answer: JWT (JSON Web Token) is a compact, URL-safe means of representing claims to be transferred between two parties. It is often used for authentication in Web API.

SignalR in Web API:

43. What is SignalR, and how is it used in Web API?

    • Answer: SignalR is a library for adding real-time functionality to applications. In Web API, it can be used to enable real-time communication between clients and the server.

44. Explain the use of hubs in SignalR.

    • Answer: Hubs in SignalR are communication endpoints that allow clients to call methods on the server and vice versa.

OData in Web API:

45. What is OData, and how is it implemented in Web API?
    • Answer: OData is an open standard for building and consuming RESTful APIs. In Web API, OData can be implemented using the Microsoft.AspNet.OData NuGet package.

Docker and Web API:

46. How can you containerize a Web API using Docker?
    • Answer: To containerize a Web API with Docker, you create a Dockerfile specifying the application, dependencies, and configuration. Then, you build an image and run containers based on that image.

Web API Design Patterns:

47. Explain the Repository Pattern and its use in Web API.

    • Answer: The Repository Pattern involves separating the logic that retrieves data from the underlying storage. It is commonly used in Web API to decouple data access code.

48. What is the role of the Unit of Work pattern in Web API?

    • Answer: The Unit of Work pattern manages the transactional boundaries and ensures that a set of operations is treated as a single unit. It is often used in conjunction with the Repository Pattern.

GraphQL and Web API:

49. What is GraphQL, and how does it differ from RESTful Web APIs?

    • Answer: GraphQL is a query language for APIs that allows clients to request only the data they need. It differs from RESTful Web APIs in that clients can specify the structure of the response.

50. How can you implement GraphQL in Web API?

    • Answer: GraphQL can be implemented in Web API using libraries such as GraphQL.NET. You define a GraphQL schema and handle queries and mutations in the API.