15 ASP.NET Web API Interview Questions And Answers

ASP.NET Web API is a framework that simplifies building HTTP services for broader range of clients (including browsers as well as mobile devices) on top of .NET Framework.

Using ASP.NET Web API, we can create non-SOAP based services like plain XML or JSON strings, etc. with many other advantages including:

• Create resource-oriented services using the full features of HTTP
• Exposing services to a variety of clients easily like browsers or mobile devices, etc.

Using ASP.NET Web API has a number of advantages, but core of the advantages are:

• It works the HTTP way using standard HTTP verbs like GET, POST, PUT, DELETE, etc. for all CRUD operations
• Complete support for routing
• Response generated in JSON or XML format using MediaTypeFormatter
• It has the ability to be hosted in IIS as well as self-host outside of IIS
• Supports Model binding and Validation
• Support for OData

• Use Controller to render your normal views.
• ApiController action only returns data that is serialized and sent to the client.

Consider:

public class TweetsController : Controller {
  // GET: /Tweets/
  [HttpGet]
  public ActionResult Index() {
    return Json(Twitter.GetTweets(), JsonRequestBehavior.AllowGet);
  }
}

or

public class TweetsController : ApiController {
  // GET: /Api/Tweets/
  public List<Tweet> Get() {
    return Twitter.GetTweets();
  }
}

By default, most exceptions are translated into an HTTP response with status code 500, Internal Server Error.

Consider:

[Route("CheckId/{id}")]
[HttpGet]
public IHttpActionResult CheckId(int id)
{
    if(id > 100)
    {
        throw new ArgumentOutOfRangeException();
    }
    return Ok(id);
}

For more control over the response, you can also construct the entire response message and include it with the HttpResponseException:

public Product GetProduct(int id)
{
    Product item = repository.Get(id);
    if (item == null)
    {
        var resp = new HttpResponseMessage(HttpStatusCode.NotFound)
        {
            Content = new StringContent(string.Format("No product with ID = {0}", id)),
            ReasonPhrase = "Product ID Not Found"
        };
        throw new HttpResponseException(resp);
    }
    return item;
}

• Windows Communication Foundation is designed to exchange standard SOAP-based messages using variety of transport protocols like HTTP, TCP, NamedPipes or MSMQ, etc.
• On the other hand, ASP.NET API is a framework for building non-SOAP based services over HTTP only.

• The purpose of Web API framework is to generate HTTP services that reach more clients by generating data in raw format, for example, plain XML or JSON string. So, ASP.NET Web API creates simple HTTP services that renders raw data.
• On the other hand, ASP.NET MVC framework is used to develop web applications that generate Views (HTML) as well as data. ASP.NET MVC facilitates in rendering HTML easy.

A Web API controller action can return any of the following:

• void - Return empty 204 (No Content)
• HttpResponseMessage - Return empty 204 (No Content)
• IHttpActionResult - Call ExecuteAsync to create an HttpResponseMessage, then convert to an HTTP response message
• Some other type - Write the serialized return value into the response body; return 200 (OK).

ASP.NET Web API v2 now support Attribute Routing along with convention-based approach. In convention-based routes, the route templates are already defined as follows:

Config.Routes.MapHttpRoute(
  name: "DefaultApi",
  routeTemplate: "api/{Controller}/{id}",
  defaults: new { id = RouteParameter.Optional }
);

So, any incoming request is matched against already defined routeTemplate and further routed to matched controller action. But it’s really hard to support certain URI patterns using conventional routing approach like nested routes on same controller. For example, authors have books or customers have orders, students have courses etc.

Such patterns can be defined using attribute routing i.e. adding an attribute to controller action as follows:

[Route("books/{bookId}/authors")]
public IEnumerable<Author> GetAuthorsByBook(int bookId) { ..... }