Top 32 ASP.NET Web API Interview Questions And Answers

Question 1

What is ASP.NET Web API?

Accepted Answer

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.

Question 2

What is the difference between `ApiController` and `Controller`?

Accepted Answer

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

Consider:
```csharp
public class TweetsController : Controller {
  // GET: /Tweets/
  [HttpGet]
  public ActionResult Index() {
    return Json(Twitter.GetTweets(), JsonRequestBehavior.AllowGet);
  }
}
```
or
```csharp
public class TweetsController : ApiController {
  // GET: /Api/Tweets/
  public List<Tweet> Get() {
    return Twitter.GetTweets();
  }
}
```

Question 3

What are the Advantages of Using ASP.NET Web API?

Accepted Answer

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

Question 4

What exactly is OAuth (Open Authorization)?

Accepted Answer

**OAuth** (Open Authorization) is an open standard for access granting/deligation protocol. It used as a way for Internet users to grant websites or applications access to their information on other websites but without giving them the passwords. It does not deal with authentication.

Basically there are three parties involved: oAuth Provider, oAuth Client and Owner.

* oAuth Client (Application Which wants to access your credential)
* oAuth Provider (eg. facebook, twitter...)
* Owner (the person with facebook,twitter.. account )

Question 5

What New Features are Introduced in ASP.NET Web API 2.0?

Accepted Answer

More new features introduced in ASP.NET Web API framework v2.0 are as follows:

*   Attribute Routing
*   External Authentication
*   CORS (Cross-Origin Resource Sharing)
*   OWIN (Open Web Interface for .NET) Self Hosting
*   `IHttpActionResult`
*   Web API OData

Question 6

Which _status code_ used for all _uncaught exceptions_ by default?

Accepted Answer

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

Consider:
```cs
[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`:
```cs
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;
}
```

Question 7

What are main _return types_ supported in Web API?

Accepted Answer

A Web API controller action can return following values:

*   `Void` – It will return empty content
*   `HttpResponseMessage` – It will convert the response to an HTTP message.
*   `IHttpActionResult` – internally calls `ExecuteAsync` to create an `HttpResponseMessage`
*   **Other types** – You can write the **serialised** return value into the response body

Question 8

Explain the usage of `HttpResponseMessage`?

Accepted Answer

A `HttpResponseMessage` allows us to work with the HTTP protocol (for example, with the headers property) and unifies our return type. In simple words an `HttpResponseMessage` is a way of returning a message/data from your action.

```cs
// GetEmployee action  
public HttpResponseMessage GetEmployee(int id)  
{  
   Employee emp = EmployeeContext.Employees.Where(e => e.Id == id).FirstOrDefault();  
   if (emp != null)  
   {  
      return Request.CreateResponse<Employee>(HttpStatusCode.OK, emp);  
   }  
   else  
   {  
      return Request.CreateErrorResponse(HttpStatusCode.NotFound, "Employee Not Found");  
   }  
}  
```

Question 9

What is Attribute Routing in ASP.NET Web API 2.0?

Accepted Answer

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:

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

Question 10

What are the differences between Web API and Web API 2?

Accepted Answer

* Attribute Routing
* OWIN self host
* `IHttpActionResult`
* CORS
* `HttpRequestContext`
* Betters Testability
* ODATA Improvements
* Filter Overrides
* `ByteRangeStreamContent`

Top 32 ASP.NET Web API Interview Questions

What is ASP.NET Web API?

Which status code used for all uncaught exceptions by default?

Explain the usage of `HttpResponseMessage`?

What New Features are Introduced in ASP.NET Web API 2.0?

What are the Advantages of Using ASP.NET Web API?

What is the difference between `ApiController` and `Controller`?

What are main return types supported in Web API?

What exactly is OAuth (Open Authorization)?

In OOP, what is the difference between the Repository Pattern and a Service Layer?

Compare WCF vs ASP.NET Web API?

Is it True that ASP.NET Web API has Replaced WCF?

Explain the difference between MVC vs ASP.NET Web API

Explain the difference between WCF RESTful Service vs ASP.NET Web API?

Name types of Action Results in Web API 2

What is Attribute Routing in ASP.NET Web API 2.0?

What are the differences between Web API and Web API 2?

Why are the `FromBody` and `FromUri` attributes needed in ASP.NET Web API?

What's the difference between OpenID and OAuth?

Explain briefly CORS (Cross-Origin Resource Sharing)?

What is ASP.NET Web API OData?

Can we use Web API with ASP.NET Web Form?

How to Return View from ASP.NET Web API Method?

What is Delegating Handler?

How to register exception filter globally?

Could you clarify what is the best practice with Web API error management?

Explain advantages/disadvantages of using `HttpModule` vs `DelegatingHandler`?

Why should I use `IHttpActionResult` instead of `HttpResponseMessage`?

Explain the difference between WCF, Web API, WCF REST and Web Service?

Explain briefly OWIN (Open Web Interface for .NET) Self Hosting?

What is difference between WCF and Web API and WCF REST and Web Service?

How to restrict access to Web API method to specific HTTP verb?

How can we provide an alias name for ASP.NET Web API Action?

Top 32 ASP.NET Web API Interview Questions

What is ASP.NET Web API?

Which status code used for all uncaught exceptions by default?

Explain the usage of HttpResponseMessage?

What New Features are Introduced in ASP.NET Web API 2.0?

What are the Advantages of Using ASP.NET Web API?

What is the difference between ApiController and Controller?

What are main return types supported in Web API?

What exactly is OAuth (Open Authorization)?

In OOP, what is the difference between the Repository Pattern and a Service Layer?

Compare WCF vs ASP.NET Web API?

Is it True that ASP.NET Web API has Replaced WCF?

Explain the difference between MVC vs ASP.NET Web API

Explain the difference between WCF RESTful Service vs ASP.NET Web API?

Name types of Action Results in Web API 2

What is Attribute Routing in ASP.NET Web API 2.0?

What are the differences between Web API and Web API 2?

Why are the FromBody and FromUri attributes needed in ASP.NET Web API?

What's the difference between OpenID and OAuth?

Explain briefly CORS (Cross-Origin Resource Sharing)?

What is ASP.NET Web API OData?

Can we use Web API with ASP.NET Web Form?

How to Return View from ASP.NET Web API Method?

What is Delegating Handler?

How to register exception filter globally?

Could you clarify what is the best practice with Web API error management?

Explain advantages/disadvantages of using HttpModule vs DelegatingHandler?

Why should I use IHttpActionResult instead of HttpResponseMessage?

Explain the difference between WCF, Web API, WCF REST and Web Service?

Explain briefly OWIN (Open Web Interface for .NET) Self Hosting?

What is difference between WCF and Web API and WCF REST and Web Service?

How to restrict access to Web API method to specific HTTP verb?

How can we provide an alias name for ASP.NET Web API Action?

Explain the usage of `HttpResponseMessage`?

What is the difference between `ApiController` and `Controller`?

Why are the `FromBody` and `FromUri` attributes needed in ASP.NET Web API?

Explain advantages/disadvantages of using `HttpModule` vs `DelegatingHandler`?

Why should I use `IHttpActionResult` instead of `HttpResponseMessage`?