Interview question and answer on ASP .Net Web API

Interview question and answer on ASP .Net Web API with full explanation and code example

Here are 40 interview questions and answers on ASP.NET Web API, along with full explanations and code examples:

1. What is ASP.NET Web API? Answer: ASP.NET Web API is a framework for building HTTP services that can be consumed by various clients, including web browsers and mobile devices.

2. What are the key features of ASP.NET Web API? Answer: Key features of ASP.NET Web API include:

   • HTTP-based services using standard HTTP verbs (GET, POST, PUT, DELETE)
   • Support for content negotiation
   • Built-in support for JSON and XML formatting
   • Flexible routing
   • Extensibility through filters and message handlers
   • Integration with ASP.NET MVC

3. How can you create a new Web API project in Visual Studio? Answer: You can create a new Web API project in Visual Studio by following these steps:

   • Open Visual Studio and select "Create a new project."
   • Choose the "ASP.NET Web Application" template.
   • Select "Web API" as the project template.
   • Configure the project settings and click "Create."

4. How do you define a Web API controller? Answer: A Web API controller is defined as a class that inherits from the ApiController class provided by the Web API framework. For example:

   csharp
   public class ProductsController : ApiController
   {
       // Controller actions and methods
   }
   

5. How do you configure routing in Web API? Answer: Routing in Web API can be configured using the MapHttpRoute method in the WebApiConfig class. For example:

   csharp
   public static class WebApiConfig
   {
       public static void Register(HttpConfiguration config)
       {
           config.Routes.MapHttpRoute(
               name: "DefaultApi",
               routeTemplate: "api/{controller}/{id}",
               defaults: new { id = RouteParameter.Optional }
           );
       }
   }
   

6. How can you handle HTTP GET requests in Web API? Answer: To handle HTTP GET requests, you can define a method in the Web API controller with the HttpGet attribute. For example:

   csharp
   public class ProductsController : ApiController
   {
       [HttpGet]
       public IHttpActionResult Get()
       {
           // Retrieve and return data
       }
   }
   

7. How can you pass parameters to a Web API controller method? Answer: Parameters can be passed to a Web API controller method in the following ways:

   • Through the URL using route parameters.
   • Through the query string.
   • Through the request body (for POST and PUT requests).

8. How can you return data from a Web API controller method? Answer: You can return data from a Web API controller method using the HttpResponseMessage class or by using the IHttpActionResult interface. For example:

   csharp
   public IHttpActionResult Get()
   {
       // Retrieve data
       var data = //...
   
       // Return data
       return Ok(data);
   }
   

9. How can you handle HTTP POST requests in Web API? Answer: To handle HTTP POST requests, you can define a method in the Web API controller with the HttpPost attribute. For example:

   csharp
   public class ProductsController : ApiController
   {
       [HttpPost]
       public IHttpActionResult Post(Product product)
       {
           // Create a new product
       }
   }
   

10. How can you handle HTTP PUT requests in Web API? Answer: To handle HTTP PUT requests, you can define a method in the Web API controller with the HttpPut attribute. For example:

    csharp
    public class ProductsController : ApiController
    {
        [HttpPut]
        public IHttpActionResult Put(int id, Product product)
        {
            // Update an existing product
        }
    }
    

11. How can you handle HTTP DELETE requests in Web API? Answer: To handle HTTP DELETE requests, you can define a method in the Web API controller with the HttpDelete attribute. For example:

    csharp
    public class ProductsController : ApiController
    {
        [HttpDelete]
        public IHttpActionResult Delete(int id)
        {
            // Delete a product
        }
    }
    

12. How can you handle model validation in Web API? Answer: Model validation can be handled in Web API by using data annotations on the model properties or by implementing custom validation logic. Additionally, you can use the ModelState property in the controller to check the validity of the model.

13. How can you return different HTTP status codes from a Web API controller method? Answer: You can return different HTTP status codes from a Web API controller method by using the HttpResponseMessage class or by returning specific IHttpActionResult instances. For example:

    csharp
    public IHttpActionResult Get()
    {
        if (someCondition)
        {
            return NotFound();
        }
    
        return Ok(data);
    }
    

14. How can you handle exceptions in Web API? Answer: Exceptions in Web API can be handled using exception filters or by implementing a global exception handler. You can create a custom exception filter by inheriting from the ExceptionFilterAttribute class.

15. What is content negotiation in Web API? Answer: Content negotiation in Web API refers to the process of selecting the appropriate response format (e.g., JSON, XML) based on the client's preferences. Web API uses the Accept header sent by the client to determine the desired format.

16. How can you enable content negotiation in Web API? Answer: Content negotiation is enabled by default in Web API. The client can specify the desired format using the Accept header, and Web API will automatically serialize the response accordingly.

17. How can you manually select the response format in Web API? Answer: You can manually select the response format in Web API by using the Request object and the CreateResponse method. For example:

    csharp
    public IHttpActionResult Get()
    {
        var data = //...
    
        if (Request.Headers.Accept.Contains(new MediaTypeWithQualityHeaderValue("application/xml")))
        {
            return ResponseMessage(Request.CreateResponse(HttpStatusCode.OK, data, "application/xml"));
        }
        else
        {
            return Ok(data);
        }
    }
    

18. How can you enable cross-origin requests (CORS) in Web API? Answer: You can enable CORS in Web API by installing the Microsoft.AspNet.WebApi.Cors package and configuring CORS in the WebApiConfig class. For example:

    csharp
    WebApiConfig{
        public static void Register(HttpConfiguration config)
        {
            config.EnableCors();
    
            // Other configuration
        }
    }
    

19. How can you handle authentication and authorization in Web API? Answer: Authentication and authorization can be handled in Web API using various approaches, such as JSON Web Tokens (JWT), OAuth, or custom authentication filters. You can also leverage ASP.NET Identity or third-party authentication providers.

20. How can you secure Web API endpoints with SSL (HTTPS)? Answer: To secure Web API endpoints with SSL, you need to configure SSL on the web server hosting your API. Additionally, you can enforce SSL for specific routes using the RequireHttps attribute.

21. How can you handle file uploads in Web API? Answer: File uploads in Web API can be handled by defining a method that accepts HttpPostedFileBase or IEnumerable<HttpPostedFileBase> as a parameter. For example:

    csharp
    public IHttpActionResult UploadFile(HttpPostedFileBase file)
    {
        // Process the uploaded file
    }
    

22. How can you implement caching in Web API? Answer: Caching in Web API can be implemented by using the CacheControl and CacheCow.Server packages. You can configure caching using attributes like CacheControl, OutputCache, or by manually setting the appropriate cache headers.

23. How can you test Web API controllers? Answer: Web API controllers can be tested using unit tests by mocking the dependencies or by creating integration tests using tools like Postman or Swagger UI.

24. What are the advantages of using IHttpActionResult over HttpResponseMessage? Answer: The IHttpActionResult interface provides a more flexible and readable way of returning HTTP responses from a Web API controller. It allows you to return different types of HTTP responses (e.g., Ok, NotFound, BadRequest) and simplifies the code by avoiding the need to create HttpResponseMessage instances manually.

25. How can you handle versioning in Web API? Answer: Versioning in Web API can be handled using URL-based versioning, query string parameter versioning, or header versioning. You can create separate controllers or use attributes like RoutePrefix and Route to handle different versions.

26. How can you log requests and responses in Web API? Answer: Requests and responses in Web API can be logged using filters or message handlers. Filters allow you to intercept requests and responses at the controller level, while message handlers allow you to intercept requests and responses globally.

27. How can you handle large payloads in Web API? Answer: To handle large payloads in Web API, you can configure the maximum request size in the web.config file or use the MaxAllowedContentLength property in the web.config file.

28. How can you handle concurrency and optimistic concurrency control in Web API? Answer: Concurrency and optimistic concurrency control can be handled in Web API by using appropriate HTTP headers (e.g., If-Match, If-None-Match) and by implementing concurrency checks in your data access layer.

29. How can you implement pagination in Web API? Answer: Pagination in Web API can be implemented by using the Skip and Take methods in your data access layer or by using query parameters to specify the page size and page number.

30. How can you handle custom error messages and error handling in Web API? Answer: Custom error messages and error handling can be implemented in Web API by creating custom exception classes, using exception filters, or by overriding the HandleException method in the ApiController class.

31. How can you implement dependency injection in Web API? Answer: Dependency injection in Web API can be implemented using third-party IoC containers like Unity, Autofac, or by using the built-in dependency resolver in ASP.NET MVC.

32. How can you handle long-running operations in Web API? Answer: Long-running operations in Web API can be handled by using asynchronous programming techniques like async and await. You can return Task<T> from your controller methods and use await to await the completion of the operation.

33. How can you handle client errors and validation errors in Web API? Answer: Client errors and validation errors can be handled in Web API by checking the ModelState property in the controller and returning appropriate error responses using the BadRequest or ModelState properties.

34. How can you handle authentication and authorization in Web API using JWT (JSON Web Tokens)? Answer: Authentication and authorization in Web API using JWT can be implemented by generating and validating JWT tokens. You can use libraries like System.IdentityModel.Tokens.Jwt or third-party libraries like IdentityServer4 to handle JWT-based authentication.

35. How can you implement rate limiting in Web API? Answer: Rate limiting in Web API can be implemented using third-party libraries like AspNetWebApiThrottle or by implementing custom logic in filters or message handlers to track and limit the number of requests per user or IP address.

36. How can you implement response compression in Web API? Answer: Response compression in Web API can be implemented by using libraries like Microsoft.AspNet.WebApi.MessageHandlers.Compression or by implementing custom message handlers to compress the response using GZIP or Deflate algorithms.

37. How can you implement custom media formatters in Web API? Answer: Custom media formatters in Web API can be implemented by creating a class that inherits from the MediaTypeFormatter class. You can override the ReadFromStreamAsync and WriteToStreamAsync methods to handle serialization and deserialization of custom media types.

38. How can you implement API versioning in Web API? Answer: API versioning in Web API can be implemented using URL-based versioning, query string parameter versioning, or header versioning. You can create separate controllers or use attributes like RoutePrefix and Route to handle different versions.

39. How can you implement content negotiation based on client preferences in Web API? Answer: Content negotiation based on client preferences in Web API can be implemented by examining the Accept header sent by the client and selecting the appropriate response format (e.g., JSON, XML) using the Request.Headers.Accept property.

40. How can you handle distributed caching in Web API? Answer: Distributed caching in Web API can be implemented using caching solutions like Redis or Memcached. You can use the IDistributedCache interface provided by ASP.NET Core or use third-party libraries like StackExchange.Redis to interact with the caching server.

These are some common interview questions and answers on ASP.NET Web API. It's important to note that the answers provided here are general and may vary depending on specific project requirements and coding practices.