Web API interview questions and answers in ASP.Net

1)What is WebAPI? (or) Explain about WebAPI

ASP.NET Web API is a framework defined by microsoft, this makes us to build HTTP services very easily

By using HTTP services we can reach more no of cutomers , different types of browsers and diffrent devices

Web API is open source for building REST-ful services

2)Explain routing in WebAPI (or) WebAPI routing ?

Like ASP.NET MVC ,IN ASP.NET Web API also controller is a class that handles HTTP requests.

When the Web API framework receives a request, its find the appropriate controller and action method to perform an action.

To determine which action to invoke, the framework uses a routing table,Which is in WebApiConfig.cs file placed in the App_Start folder in project.

routes.MapHttpRoute(
    name: "API Default",
    routeTemplate: "api/{controller}/{id}",
    defaults: new { id = RouteParameter.Optional }
);

From above "api" is a literal path segment, and {controller} and {id} are placeholder variables.

3) What is the difference between MVC Routing and Web API Routing?

WebAPI routing structure in WebApiConfig.cs:

routes.MapHttpRoute(
    name: "API Default",
    routeTemplate: "api/{controller}/{id}",
    defaults: new { id = RouteParameter.Optional }
);

MVC routing structure in RouteConfig.cs:

    routes.MapRoute(
                    name: "Default",
                    url: "{controller}/{action}/{id}",
                    defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
                );

In WebAPI route "api" string literal is prefixed for route.

In WebAPI route {action} place holder is optional

4) How parameter binding works in Web API?

Below are the rules followed by WebAPI before binding parameters –

1)If it is simple parameters like – bool,int, double etc. then value will be obtained from the URL.
2)Value read from message body in case of complex types.

5)Action Results in WebAPI ?

void : Nothing return
HttpResponseMessage : Convert directly to HTTp Response message
IHttpActionResult : Call ExecuteAsync to create an HttpResponseMessage, then convert to an HTTP response message.
Some other type : Write a serialized return value

HttpResponseMessage Example :

 public HttpResponseMessage GetData()
    {
        HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK, "value");
        response.Content = new StringContent("hello", Encoding.Unicode);
        response.Headers.CacheControl = new CacheControlHeaderValue()
        {
            MaxAge = TimeSpan.FromMinutes(20)
        };
        return response;
    }

public HttpResponseMessage GetData()
{
    // Get a list of Students from a database.
    IEnumerable<Student> students = GetStudentsFromDB();

    // Write the list to the response body.
    HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK, students);
    return response;
}

IHttpActionResult:

It defines an HttpResponseMessage

Simplifies unit testing your controllers.
Moves common logic for creating HTTP responses into separate classes.
Makes the intent of the controller action clearer, by hiding the low-level details of constructing the response.

public class MyResult : IHttpActionResult
{
    string _value;
    HttpRequestMessage _request;

    public MyResult(string value, HttpRequestMessage request)
    {
        _value = value;
        _request = request;
    }
    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage()
        {
            Content = new StringContent(_value),
            RequestMessage = _request
        };
        return Task.FromResult(response);
    }
}

public class ValuesController : ApiController
{
    public IHttpActionResult Get()
    {
        return new MyResult("Pass", Request);
    }
}

6)Routing table syntax in WebAPI ?

routes.MapHttpRoute(
    name: "API Default",
    routeTemplate: "api/{controller}/{id}",
    defaults: new { id = RouteParameter.Optional }
);

If no route matches, the client receives a 404 error.

Instead of using Naming conventions on action method , use HTTP action methods like HttpGet, HttpPut, HttpPost, or HttpDelete attribute.

To allow multiple HTTP methods for one action use the AcceptVerbs attribute, which takes a list of HTTP methods.

7)How to ignore the actions WebAPI?

[NonAction] attribute ,we can ignore the actions.

8)How parmeters gets the value in WebAPI ?

Using the following way parameters get the values

1) URI
2) Request body
3) Custom Binding

9)How to enable Attribute routing ?

TO enable attribute routing, call MapHttpAttributeRoutes(); method in WebApi config file.

 public static void Register(HttpConfiguration config)
        {
            // Web API routes
            config.MapHttpAttributeRoutes();

            // Other Web API configuration not shown.
        }

10)Can we apply constraints at route level ?

Yes we can apply.

[Route("students/{id:int}"]
public User GetStudentById(int id) { ... }

[Route("students/{name}"]
public User GetStudentByName(string name) { ... }

From above Here, the first route will only be selected whenever the "id" segment of the URI is an integer. Otherwise, the second route will be chosen.

11)How to mention Roles and users using Authorize attribute in Web API?

// Restrict by Name
[Authorize(Users="Shiva,Jai")]
public class StudentController : ApiController
{
}
 
// Restrict by Role
[Authorize(Roles="Administrators")]
public class StudnetController : ApiController
{
}

12)How to enable SSL to ASP.NET web?

To enable SSL to ASP.NET web , click project properties there you can see this option.

13)How to add certificates to website?

go to run type command mmc click on ok then its opend certificate add window

14)Write a LINQ code for authenticate the user?

public static bool Login(string UN, string pwd)
{
StudentDBEntities students = new StudentDBEntities()
students.sudent.Any(e => e.UserName.Equals(UN) && e=>e.Password.Equlas(UN)) // students has morethan one table
}

15)How to navigate other page in JQuery?

using widow.location.href = "~/homw.html";

16)Exception handling in WebAPI?

The HttpResponseException most common exception in WebAPI.

public Product GetStudentDetails(int rno)
{
    Student studentinfo = repository.Get(rno);
    if (studentinfo == null)
    {
        throw new HttpResponseException(HttpStatusCode.NotFound);
    }
    return studentinfo;
}

using exception filters we can handle the exceptions at action method level or controller level

if you want to apply any filter to entire application , register the filter in WebAPI confil file

using Exception hadlers and Exception loogers aslo can handle the Exceptions

17) What is NonActionAttribute class in WebAPI?

If we want to restrict the particular actionmethod accessing from browser, we can NonAction attribute.public ActionResult 

[NonAction]
public ActionResult Insert(){
    return View();
}

Above method not getting access from browser 

18) How parameter binding works in Web API?

Below are the rules followed by WebAPI before binding parameters –

1)If it is simple parameters like – bool,int, double etc. then value will be obtained from the URL.
2)Value read from message body in case of complex types.


19)What is the difference between SOAP and REST?

SOAP
----
SOAP is a protocal , communication should be done in the form of XML

SOAP based reads cannot be cached 

Slower than rest

REST
----
Rest is architectual pattren , supports many data pattrens

Rest reads can be cached

Fater than SOAP

20)Which top 5 New Features have been included in ASP.NET Web API 2?

1.Attribute Routing,
2.Web API OData
3.CORS ? Cross Origin Resource Sharing,
4.IHttpActionResult
5.OWIN (Open Web Interface for .NET) self hosting,

21)What are different status codes available in web?

1**: Informational-It means the request has been received and the process is continuing.
2**: Success
3**: Redirection-It means further action must be taken in order to complete the request.
4**: ClientError-It means the request contains incorrect syntax or cannot be fulfilled
5**: ServerError

22)Use of AllowAnonymousAttribute Class in WebAPI?

Use of we can skip the Authentication and authorizaion for a action method. It is not asking credintial while accessing a action method

Authorize]
public class StudentController : Controller {
  [AllowAnonymous]
  public ActionResult Login() 
  {
    // ...
  }

  [AllowAnonymous]
  public ActionResult Register()
 {
    // ...
  }

23)Use of FromUri attribute in web api ? (and) Use of FromBody attribute in web api?

Bydefault in WebAPI reads the simple parameters like int,bool,long, string,date..etc... form URI
Bydefault in WebAPI reads the Complex parameters like objects form body
Above is the default behaviour , if want to override default then you can use FromBody,FromUri attributes 

FromUri attribute that specifies that an action parameter comes from the URI of incoming request

    public HttpResponseMessage Post([FromUri] int id)
    {

    }

FromBody attribute that specifies that an action parameter comes only from the entity body of the incoming request

    public HttpResponseMessage Post([FromBody]int id)
    {

    }

24)What is the use of HttpBindNever attribute Class in webapi example?

public class Student
{
[HttpBindNever]
Public int studentno{get;set;}
[Required]
Public string studentName {get;set;}
}

HttpBindNever attribute, which prevents Web API from assigning a value to a property from the request. 

This ensures I don’t get unexpected or undesired behavior by accepting request values for properties that I need to set in the application.

In the above example i dont want to set stdentno property, So that i am using HttpBindNever attribute.

25)Use of HttpError Class in WebAPI?

It is a container for storing error information. This information is stored as key/value pairs.

public HttpResponseMessage GetStudentDetails(int rno)
{
    Student studentinfo = Collegerepository.Get(id);
    if (item == null)
    {
        var message = string.Format("Student with Roll Number = {0} not found", rno);
        HttpError err = new HttpError(message);
        return Request.CreateResponse(HttpStatusCode.NotFound, err);
    }
    else
    {
        return Request.CreateResponse(HttpStatusCode.OK, studentinfo);
    }
}

                                                    For  Part2 click here

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