WCF - Top 10 Interview Questions

What are the important principles of SOA (Service oriented Architecture)?

What are ends, contract, address, and bindings?

Which specifications does WCF follow?

What are the main components of WCF?

Explain how Ends, Contract, Address, and Bindings are done in WCF?

What is a service class?

What is a service contract, operation contract and Data Contract?

What are the various ways of hosting a WCF service?

How do we host a WCF service in IIS?

What are the advantages of hosting WCF Services in IIS as compared to self-hosting?

What are the major differences between services and Web services?

What is the difference WCF and Web services?

What are different bindings supported by WCF?

Which are the various programming approaches for WCF?

What is one-way operation?

Can you explain duplex contracts in WCF?

How can we host a service on two different protocols on a single server?

How can we use MSMQ bindings in WCF?

Can you explain transactions in WCF?

What different transaction isolation levels provided in WCF?

Can we do transactions using MSMQ?

Can we have two-way communications in MSMQ?

What are Volatile queues?

What are Dead letter queues?

What is a poison message?

1. What is the difference between WCF and ASMX Web Services?

Simple and basic difference is that ASMX or ASP.NET web service is designed to send and receive messages using SOAP over HTTP only. While WCF can exchange messages using any format (SOAP is default) over any transport protocol (HTTP, TCP/IP, MSMQ, NamedPipes etc).

Another tutorial WCF Vs ASMX has detailed discussion on it.

2. What are WCF Service Endpoints? Explain.

For Windows Communication Foundation services to be consumed, it’s necessary that it must be exposed; Clients need information about service to communicate with it. This is where service endpoints play their role.

A WCF service endpoint has three basic elements i.e. Address, Binding and Contract.

• Address: It defines "WHERE". Address is the URL that identifies the location of the service.
• Binding: It defines "HOW". Binding defines how the service can be accessed.
• Contract: It defines "WHAT". Contract identifies what is exposed by the service.

3. What are the possible ways of hosting a WCF service? Explain.

For a Windows Communication Foundation service to host, we need at least a managed process, a ServiceHost instance and an Endpoint configured. Possible approaches for hosting a service are:

1. Hosting in a Managed Application/ Self Hosting
   1. Console Application
   2. Windows Application
   3. Windows Service
2. Hosting on Web Server
   1. IIS 6.0 (ASP.NET Application supports only HTTP)
   2. Windows Process Activation Service (WAS) i.e. IIS 7.0 supports HTTP, TCP, NamedPipes, MSMQ.

4. How we can achieve Operation Overloading while exposing WCF Services?

By default, WSDL doesn’t support operation overloading. Overloading behavior can be achieved by using "Name" property of OperationContract attribute.

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[ServiceContract]
interface IMyCalculator
{
   [OperationContract(Name = "SumInt")]
   int Sum(int arg1,int arg2);

   [OperationContract(Name = "SumDouble")]
   double Sum(double arg1,double arg2);
}

When the proxy will be generated for these operations, it will have 2 methods with different names i.e. SumInt and SumDouble.

5. What Message Exchange Patterns (MEPs) supported by WCF? Explain each of them briefly.

1. Request/Response 2. One Way 3. Duplex

Request/Response

It’s the default pattern. In this pattern, a response message will always be generated to consumer when the operation is called, even with the void return type. In this scenario, response will have empty SOAP body.

One Way

In some cases, we are interested to send a message to service in order to execute certain business functionality but not interested in receiving anything back. OneWay MEP will work in such scenarios. If we want queued message delivery, OneWay is the only available option.

Duplex

The Duplex MEP is basically a two-way message channel. In some cases, we want to send a message to service to initiate some longer-running processing and require a notification back from service in order to confirm that the requested process has been completed.

6. What is DataContractSerializer and How its different from XmlSerializer?

Serialization is the process of converting an object instance to a portable and transferable format. So, whenever we are talking about web services, serialization is very important.

Windows Communication Foundation has DataContractSerializer that is new in .NET 3.0 and uses opt-in approach as compared to XmlSerializer that uses opt-out. Opt-in means specify whatever we want to serialize while Opt-out means you don’t have to specify each and every property to serialize, specify only those you don’t want to serialize. DataContractSerializer is about 10% faster than XmlSerializer but it has almost no control over how the object will be serialized. If we wanted to have more control over how object should be serialized that XmlSerializer is a better choice.

7. How we can use MessageContract partially with DataContract for a service operation inWCF?

MessageContract must be used all or none. If we are using MessageContract into an operation signature, then we must use MessageContract as the only parameter type and as the return type of the operation.

8. Which standard binding could be used for a service that was designed to replace an existing ASMX web service?

The basicHttpBinding standard binding is designed to expose a service as if it is an ASMX/ASP.NET web service. This will enable us to support existing clients as applications are upgrade to WCF.

9. Please explain briefly different Instance Modes in WCF?

WCF will bind an incoming message request to a particular service instance, so the available modes are:

• Per Call: instance created for each call, most efficient in term of memory but need to maintain session.
• Per Session: Instance created for a complete session of a user. Session is maintained.
• Single: Only one instance created for all clients/users and shared among all.Least efficient in terms of memory.

10. Please explain different modes of security in WCF? Or Explain the difference between Transport and Message Level Security.

In Windows Communication Foundation, we can configure to use security at different levels

a. Transport Level security means providing security at the transport layer itself. When dealing with security at Transport level, we are concerned about integrity, privacy and authentication of message as it travels along the physical wire. It depends on the binding being used that how WCF makes it secure because most of the bindings have built-in security.

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            <netTcpBinding>
            <binding name="netTcpTransportBinding">
               <security mode="Transport">
                          <Transport clientCredentialType="Windows" />
               </security>
            </binding>
            </netTcpBinding>

b. Message Level Security For Tranport level security, we actually ensure the transport that is being used should be secured but in message level security, we actually secure the message. We encrypt the message before transporting it.

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             <wsHttpBinding>
             <binding name="wsHttpMessageBinding">
               <security mode="Message">
                           <Message clientCredentialType="UserName" />
               </security>
              </binding>
             </wsHttpBinding>

It totally depends upon the requirements but we can use a mixed security mode also as follows:

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             <basicHttpBinding>
             <binding name="basicHttp">
               <security mode="TransportWithMessageCredential">
                          <Transport />
                               <Message clientCredentialType="UserName" />
               </security>
             </binding>
             </basicHttpBinding>

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Interview questions on asp net c# for 2 years experience

1 :-  How is Felling know ?
Asn :- Good ,Felling well like this you give the answer

2  :- Tell me about your self in brief ?
Good morning sir/madam.

This is Saurabh Hangotra

I have completed my 10th standard in 2004 from  St Josephs Convent school and also 12th standard in 2006.

I have completed my graduation in 2010 from Patel college of science & Technology.


Coming to my family background.

My father is a retired government employee in Western Railways as Chief Ticket Inspector(CTI).

My mother is a housewife.

I have 2 elder sister.

My personal details are.

My strength are hardworking and truth person.

My weakness are emotional and a little shy.

My hobbies are playing cricket, surfing, chess.

Thank you.
3 :- What is asp.net life cycle ?

Life Cycle Events

PreInit

The properties like IsPostBack have been set at this time.

This event will be used when we want to:

1. Set master page dynamically.
2. Set theme dynamically.
3. Read or set profile property values.
4. This event is also preferred if want to create any dynamic controls.

Init

1. Raised after all the controls have been initialized with their default values and any skin settings have been applied.
2. Fired for individual controls first and then for page.

LoadViewState

1. Fires only if IsPostBack is true.
2. Values stored in HiddenField with id as _ViewState decoded and stored into corresponding controls.

LoadPostData

Some controls like:

1. Fires only if IsPostBack is true.
2. Some controls like Textbox are implemented from IPostBackDataHandler and this fires only for such controls.
3. In this event page processes postback data included in the request object pass it to the respective controls.

PreLoad

• Used only if want to inject logic before actual page load starts.

Load

• Used normally to perform tasks which are common to all requests, such as setting up a database query.

Control events

1. This event is fired when IsPostBack is true.
2. Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event.

PreRenderRaised after the page object has created all the controls that are required for rendering which includes child controls and composite controls.

1. Use the event to make final changes to the contents of the page or its controls before the values are stored into the viewstate and the rendering stage begins.
2. Mainly used when we want to inject custom JavaScript logic.

SaveViewState

• All the control values that support viewstate are encoded and stored into the viewstate.

RenderGenerates output (HTML) to be rendered at the client side.

• We can add custom HTML to the output if we want here.

Unload

1. Fired for individual controls first and then for page.
2. Used to perform cleanup work like closing open files and database connections.

5 :- How the request is handled by IIS ?

We give an URL to an aspx page in the browser address bar and press enter. What happens next? We get the response in terms of rendered HTML but how?

1. We are requesting something from the browser, which means indirectly we are requesting something from the Web Server, that means IIS. IIS, based on the file extension, decides which ISAPI extension can serve the request.
   
   And in case of ASP.Net (.aspx) it will be aspnet_isapi_dll so the request is passed to it for processing.
    
2. When the first request comes to the website,
   
   an application domain is created by the ApplicationManager class where exactly the website runs, and which creates an isolation between 2 web applications.
   Within the application domain an instance of the HostingEnvironment class is created which provides access information about the application such as the name of the folder where the application is stored.
    
3. Next ASP.Net creates core objects like HttpContext, HttpRequest,HttpResponse.
    
4. Finally the application starts by creating an instance of the HttpApplication Class (which can be reused for multiple requests to maximize performance).

6 :- difference between form authentication and windows authentication asp net ?
ans - ASP.NET has ways to Authenticate a user:

1) Forms Authentication :-
 Form authentication is used for internet and intranet based application.
This is provided so that web pages can make use of the local Windows User and Groups .

2) Windows Authentication :-
Windows authentication is the default authentication provided by the .net framework.


Windows Authentication provider is the default authentication provider for ASP.NET applications. When a user using this authentication logs in to anapplication, the credentials are matched with the Windows domain through IIS.


There are 4 types of Windows Authentication methods:
1) Anonymous Authentication - IIS allows any user
2) Basic Authentication - A windows username and password has to be sent across the network (in plain text format, hence not very secure).
3) Digest Authentication - Same as Basic Authentication, but the credentials are encrypted. Works only on IE 5 or above
4) Integrated Windows Authentication - Relies on Kerberos technology, with strong credential encryption



Forms Authentication - This authentication relies on code written by a developer, where credentials are matched against a database. Credentials are entered on web forms, and are matched with the database table that contains the user information.

7 :- what is authentication and authorization in .net ? 
ans :- Authentication And Authorization
Authentication is the process of identification and validation of a user's credentials. After the identity is authenticated,
a process called authorization determines whether that identity has access to a particular resource.
ASP.NET provides three ways to authenticate a user:
Forms authentication
Windows authentication
Passport authentication

Setting in web.config file given below

Forms authentication
<configuration>
<system.web>
<authentication mode="Forms"/>
<forms name="login"loginUrl="loginPage.aspx" />
<authorization>
<deny users="?"/>
</authorization>
</system.web>
</configuration>

Windows authentication
<authentication mode="Windows"/>
<authorization>
<allow users ="*" />
</authorization>

Passport authentication
<configuration>
<system.web>
<authenticationmode="Passport">
<passportredirectUrl="loginPage.aspx" />
</authentication>
<authorization>
<deny users="?" />
</authorization>
</system.web>
</configuration>



8 :- What is Difference between Session and Cookies  ? 

The basic and main difference between cookie and session is that cookies are stored in the user's browser but sessions can't store in user's browser. This specifies which is best used for.

• A cookie can keep all the information in the client's browser until deleted. If a person has a login and password, this can be set as a cookie in their browser so they do not have to re-login to your website every time they visit. You can store almost anything in a browser cookie.

• Sessions are not reliant on the user allowing a cookie. They work like a token in the browser which allowing access and passing information while the user has opened his browser. The problem in sessions is when you close the browser the session will automatically lost. So, if you had a site requiring a login, this couldn't be saved as a session but it can be saved as a cookie, and the user has to re-login every time they visit.
cookies are nothing but a small piece of information on the client machine. before we create a cookies we should check whether the cookies are allowed at the browser side. They are limited in a size 4k.(they are 2 types of cookies peristant cookie , and session cookies)

Sessions cookies are stored in a server memory during the client browser session.When the browser is closed the session cookies are lost.

9 :-Advantages and disadvantages of Session?
Following are the basic advantages and disadvantages of using session. I have describe in details with each type of session at later point of time.

Advantages:

• It helps maintain user state and data all over the application.
• It is easy to implement and we can store any kind of object.
• Stores client data separately.
• Session is secure and transparent from the user.

Disadvantages:

• Performance overhead in case of large volumes of data/user, because session data is stored in server memory.
• Overhead involved in serializing and de-serializing session data, because in the case of StateServer and SQLServer session modes, we need to serialize the objects before storing them.

Besides these, there are many advantages and disadvantages of session that are based on the session type. I have discussed all of them in the respective sections below.

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