WCF Interview Questions and Answers

Question 1: What is WCF?

Answer:

WCF is a platform for building distributed businesses and deploying services among various endpoints in Windows. WCF was initially called “Indigo” and we can build service-oriented applications and provide interoperability.

WCF or Windows Communication Foundation is a programming model to create service oriented applications. It is used to create and deploy the service that is accessible to lots of different clients. It provides an environment where you can create a service which can be accessible to Windows clients as well as Linux clients or any others. It provides more features compared to web services.

WCF is a Microsoft technology to create service oriented application. Before the WCF, the Web Service was used to create services but that type of service is only accessible to Windows client hosted on HTTP protocol. But WCF services are accessible with different protocols like http, tcp, msmq, etc. A few sample scenarios include:

For more details visit the following link:

• Introduction to WCF

Question 2: Explain WCF Architecture and also explain its Fundamentals?

Answer

Windows Communication Foundation (WCF) is a framework for building service-oriented applications by which we can send asynchronous message/data from one service endpoint to another service endpoint.

WCF is a runtime and a set of APIs for creating systems that sends messages between services and clients. The same infrastructure and APIs are used to create applications that communicate with other applications on the same computer system or on a system that resides in another company and is accessed over the Internet.

The WCF fundamentals are as follows:

• Unification
  
  • COM+ Services
  • Web Services
  • .NET Remoting
  • Microsoft Message Queuing
    
• Interoperability
• Service Orientation

WCF Architecture

There are four major layers that provide developers with a new service-oriented programming model. The WCF architecture consists of the following layers.

For more details visit following link:

• A Beginner's Tutorial For Understanding WCF

Question 3: Why Should We Use WCF Service?

Answer

Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Most of WCF functionality is included in a single assembly called System.ServiceModel.dll, located in the System.ServiceModel namespace.

Why WCF

1. A web service to exchange messages in XML format using HTTP protocol for interoperability.
2. A remoting service to exchange messages in binary format using TCP protocol for performance.
   • A secure service to process business transactions.
   • A service that supplies current data to others, such as a traffic report or other monitoring service.
   • A chat service that allows two people to communicate or exchange data in real time.
   • A dashboard application that polls one or more services for data and presents it in a logical presentation.
   • A Silverlight application to poll a service for the latest data feeds.

For more details visit the following link:

• Introduction to WCF: Part 1

Question 4: What are the features and advantage of WCF?

Answer

Features of WCF

Windows Communication Foundation (WCF) is a secure, reliable, and scalable messaging platform for the .NET Framework 3.0,

• Service Orientation
• Interoperability
• Multiple Message Patterns
• Service Metadata
• Data Contracts
• Security
• Multiple Transports and Encodings
• Reliable and Queued Messages
• Durable Messages
• Transactions
• AJAX and REST Support
• Extensibility

Advantages of WCF

1. Service Oriented
2. Location Independent
3. Language Independent
4. Platform Independent
5. Support Multiple operation
6. WCF can maintain transaction like COM+ Does
7. It can maintain state
8. It can control concurrency
9. It can be hosted on IIS, WAS, Self hosting, Windows services.

It has AJAX Integration and JSON (JavaScript object notation) support.

• WCF can be configured to work independently of SOAP and use RSS instead.
• WCF is one of the fastest communication technologies and offers excellent performance compared to other Microsoft specifications.
• To improve communication, transmission speed needs to be optimized. This is done by transmitting binary-coded XML data instead of plain text to decrease latency.
• Object life-cycle management and distributed transaction management are applicable to any application developed using WCF.

For more details visit the following link:

• WCF Learning Series: Part 1

Question 5: What is the difference between WCF and Web services?

Answer: WCF

Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another.

Web Services: A Web Service is programmable application logic accessible via standard web protocols. One of these web protocols is the Simple Object Access Protocol (SOAP). SOAP is a W3C submitted note (as of May 2000) that uses standards based technologies (XML for data description and HTTP for transport) to encode and transmit application data.

For more details visit the following link:

• What are the difference between WCF and Web Services?

Question 6: Explain what is SOA? Are web-services SOA?

Answer:

SOA

SOA stands for service oriented architecture. Service Oriented Architecture is an architectural approach in software development where the application is organized as "Services". Services are a group of methods that contain the business logic to connect a DB or other services. For instance you go to a hotel and order food. Your order first goes to the counter and then it goes to the kitchen where the food is prepared and finally the waiter serves the food.

Some important characteristics of Service Oriented Architecture

• SOA services should be independent of other services.
  Altering a service should not affect the client calling the service.
  
• Services should be self-contained.
  
  • Services should be able to define themselves (in the Web Service Description Language (WSDL)). Services should be able to describe what they do. It should be able to tell the client what all of the operations it does, what are all the data types it uses and what kind of value it will return.

SOA Overview: A Service Oriented Architecture is based on four key abstractions.

• An Application Front End
• A Service
• A Service Repository
• A Service Bus

Application Front End: The application front end is decoupled from the services. Each service has a contract that defines what it will do and one or more interfaces to implement the contract.

A Service: It has the methods with the defined contracts and the implementation of the business logic to connect the DB or other service.

A Service Repository: The service repository provides a home for the services and the service bus provides an industry-standard mechanism for connecting to and interacting with the services.

Are web-services SOA?

SOA is thinking, it's an architectural concept and web service is one of the technical approach to complete it. Web services are the preferred standards to achieve SOA.

• In SOA we need the services to be loosely coupled. A web service communicates using SOAP protocol which is XML based which is very loosely coupled. SOA services should be able to describe themselves. WSDL describes how we can access the service.
• SOA services are located in a directory. UDDI describes where we can get the web service. This nothing but implementation of SOA registry.

For more details visit the following link:

• Service Oriented Architecture: SOA

Question 7:What is Service Contract in WCF?

Answer: Service contract means the collective mechanisms by which a service's capabilities and requirements are specified for its consumers. We must say that it defines the operations that a service will perform when executed. It tells more things about a service, like message data types, operation locations, the protocols the client will need in order to communicate with the service.

To create a service contract you define an interface with related methods representative of a collection of service operations, and then decorate the interface/class with the ServiceContract Attribute to indicate it is a service contract. Methods in the interface that should be included in the service contract are decorated with the OperationContract Attribute.

How to define a Service Contract

ServiceContractAttribute: It is used to declare the type as a Service Contract. It can be declared without any parameters but it can also take named parameters.

[ServiceContract(Name="MyService", Namespace="https://tempuri.org")]  
public interface IMyService  
{  
   [OperationContract]  
   int AddNum(string numdesc, string assignedTo);  
}

OperationContractAttribute: It can only be applied on methods. It is used to declare methods which belong to a Service Contract. It controls the service description and message formats.

For more details visit the following link:

• Service Contract in WCF

Question 8: What are Contracts in WCF? How many Contracts are in WPF?

Answer: The main use of contracts is to allow the client and services agree as to the types of operations and structures they will use during the communication process. It also shows the formal agreements between client and service to define a platform-neutral and standard for describing that what the service does.

Service Contract

A service contract defines the operations which are exposed by the service to the outside world. A service contract is the interface of the WCF service and it tells the outside world what the service can do. It may have service-level settings, such as the name of the service and namespace for the service.

Operation Contract

An Operation Contract defines the method exposed to the client to exchange the information between the client and server. An Operation Contract describes what functionality is to be given to the client, such as addition, subtraction and so on.

It can be defined as in the following:

public interface IService1  
{  
    [OperationContract]  
    string GetData(int value);  
    [OperationContract]  
    CompositeType GetDataUsingDataContract(CompositeType composite);  
}

Data Contract

Data Contracts define the data type for variables that are the same as get and set properties but the difference is that a Data Contract in WCF is used to serialize and deserialize the complex data. It defines how data types are serialized and deserialized. Using serialization, you can convert an object into a sequence of bytes that can be transmitted over a network. Using de-serialization, you reassemble an object from a sequence of bytes that you receive from a calling application.

Example

DataContract

public class Student  
{  
    private string _Name;  
    private string _City;  
    [DataMember]  
    public string Name  
    {  
        get  
        {  
            return _Name;  
        }  
        set  
        {  
            _Name = value;  
        }  
    }  
}

Message Contract

When an operation contract required to pass a message as a parameter or return value as a message, the type of this message will be defined as message contract. A message contract defines the elements of the message (like as Message Header, Message Body), as well as the message-related settings, such as the level of message security.

Message contracts give you complete control over the content of the SOAP header, as well as the structure of the SOAP body.

Fault Contract

A fault contract defines errors raised by the service, and how the service handles and propagates errors to its clients. An operation contract can have zero or more fault contracts associated with it.

The following is the syntax to raise the custom error in WCF:

[ServiceContract]  
public interface IGetDetailsService  
{  
    [OperationContract]  
    [FaultContract(typeof (Student))]  
    Student GetDetails(string Name);  
}  
[DataContract]  
public class Student  
{  
    private string _Name;  
    private string _City;  
    [DataMember]  
    public string Name  
    {  
        get  
        {  
            return _Name;  
        }  
        set  
        {  
            _Name = value;  
        }  
    }  
    [DataMember]  
    public string City  
    {  
        get  
        {  
            return _City;  
        }  
        set  
        {  
            _City = value;  
        }  
    }  
}

For more details visit the following link:

• Contracts in WCF Service

Question 9: What is Data Contract in WCF?

Answer: A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged.

Data contract can be explicit or implicit. Simple type such as int, string etc has an implicit data contract. User defined object are explicit or Complex type, for which you have to define a Data contract using [DataContract] and [DataMember] attribute.

A data contract can be defined as follows:

• It describes the external format of data passed to and from service operations.
• It defines the structure and types of data exchanged in service messages.
• It maps a CLR type to an XML Schema.
• It defines how data types are serialized and deserialized. Through serialization, you convert an object into a sequence of bytes that can be transmitted over a network. Through deserialization, you reassemble an object from a sequence of bytes that you receive from a calling application.
• It is a versioning system that allows you to manage changes to structured data.

[DataContract]   
public class CuboidInfo   
{   
}

For more details visit the following link:

• Data Contract in WCF

Question 10: What is Message Contract in WCF?

Answer

A Message Contract is used to control the structure of a message body and serialization process. It is also used to send / access information in SOAP headers. By default WCF takes care of creating SOAP messages according to service DataContracts and OperationContracts.

A MessageContract controls the structure of a message body and serialization process. A MessageContract can be typed or untyped and are useful in interoperability cases and when there is an existing message format we must comply with.

The SOAP header is implemented in the namespace system.web.services.protocol.

[MessageContract]  
public class AutherRequest  
{  
   public string AutherId;  
}

Message Header

A Message Header is applied to a member of a message contract to declare the member within the message header.

[MessageContract]  
public class AutherRequest  
{  
   [MessageHeader]  
   public string AutherId;  
}

Message Body Member

A Message Body Member is applied to the member of a message contract to declare the members within the message body.

[MessageContract]  
public class AuthorResponse  
{  
    [MessageBodyMember]  
    public Auther Obj;  
}

For more details visit the following link:

• How to Implement Message Contract in WCF

Question 11: What is Fault Contract in WCF?

Answer

Fault Contract provides documented view for error accorded in the service to client. This help as to easy identity the what error has occurred, and where. By default when we throw any exception from service, it will not reach the client side. The less the client knows about what happened on the server side, the more dissociated the interaction will be, this phenomenon (not allowing the actual cause of error to reach client) is known as error masking. By default all exceptions thrown on the service side always reach the client as FaultException, as by having all service exceptions indistinguishable from one another, WCF decouples the client from service.

Syntax

[OperationContract]
[FaultContract(typeof(MyException))]
string getDetails(int value);

For more details visit the following link:

• How to Implement Fault Contract in WCF

Question 12: What is End Points and how many types of End points?

Answer

Endpoints provide the configuration required for the communication and create the complete WCF service application.

An Endpoint is a piece of information that tells WCF how to build the runtime communication channels to send and receive messages. An endpoint consists of the three things address, binding and contract.

All communication with a Windows Communication Foundation (WCF) service occurs through the endpoints of the service. Endpoints provide clients access to the functionality offered by a WCF service.

Each endpoint consists of four properties:

• An address that indicates where the endpoint can be found.
• A binding that specifies how a client can communicate with the endpoint.
• A contract that identifies the operations available.

The Structure of an Endpoint-

Each endpoint consists of the following:

• A set of behaviors that specify local implementation details of the endpoint.
  
• Address: The address uniquely identifies the endpoint and tells potential consumers of the service where it is located. It is represented in the WCF object model by the EndpointAddress class. An EndpointAddress class contains:
  
  • A Uri property, which represents the address of the service.
  • An Identity property, which represents the security identity of the service and a collection of optional message headers. The optional message headers are used to provide additional and more detailed addressing information to identify or interact with the endpoint.
    
• Binding: The binding specifies how to communicate with the endpoint. This includes:
  
  • The transport protocol to use (for example, TCP or HTTP).
  • The encoding to use for the messages (for example, text or binary).
  • The necessary security requirements (for example, SSL or SOAP message security).
    
• Contracts: The contract outlines what functionality the endpoint exposes to the client. A contract specifies:
  
  • What operations can be called by a client.
  • The form of the message.
  • The type of input parameters or data required to call the operation.
  • What type of processing or response message the client can expect.
    
    

For more details visit the following link:

• Introduction To WCF Endpoints

Question 13: What is Address in WCF?

Answer: Address - Where - Where to send messages

An Address is a unique Uniform Resource Locator (URI) that identifies the location of the service. It defines the network address for sending and receiving the messages. It is divided into four parts:

In WCF every service are associated with unique address. The address provided two imported elements the location of services and the transport protocol which will help to communicate with the services .WCF support the following transport schemes. Here is the answer for what are the supported transport protocols in WCF.

• HTTP/HTTPS
• TCP
• IPC
• Peer Network
• MSMQ
• Service BUS

Let us see here what is the format of an address in WCF?

Address always have the following format.

[transport]://[machine or domain][:optional port].
ex: https://localhost:82/MyService

For more details visit the following link:

• ABCs of WCF

Question 14: What is Binding in WCF?What are the types of binding?

Answer: Binding describes how client will communicate with service. There are different protocols available for the WCF to communicate to the Client. You can mention the protocol type based on your requirements.

A binding has several characteristics, including the following:

• Transport - Defines the base protocol to be used like HTTP, Named Pipes, TCP, and MSMQ are some type of protocols.
  
• Encoding (Optional) - Three types of encoding are available-Text, Binary, or Message Transmission Optimization Mechanism (MTOM). MTOM is an interoperable message format that allows the effective transmission of attachments or large messages (greater than 64K).
  
• Protocol(Optional) - Defines information to be used in the binding such as Security, transaction or reliable messaging capability.

The following table gives some list of protocols supported by WCF binding.

For more details visit the following link:

• Different Types Of Bindings In WCF

Question 15: Explain transactions in WCF?

Answer

A transaction is a logical unit of work consisting of multiple activities that must either succeed or fail together. For example, you are trying to make an online purchase for a dress; your amount is debited from the bank, but your ordered dress was not delivered to you. So what did you get from the preceding example? Bank operations hosted in a separate service and the online purchase service (Ordering the goods) hosted as another separate service. For the preceding example the online purchase service did not work well as expected due to the database query error, without knowing it the Bank operations were completed perfectly. For this we really need transactions to ensure that either of the operations should succeed or fail. Before we go to the WCF transactions, let us discuss what exactly are the basics behind the transactions.

The following are the types of the Transactions:

1. Atomic
2. Long Running

Phases of WCF Transaction

There are two phases in a WCF transaction as shown in the following figure.

• Prepare Phase - In this phase, the transaction manager checks whether all the entities are ready to commit for the transaction or not.
• Commit Phase - In this phase, the commitment of entities get started in reality.

For more details visit the following link:

• Service Behavior in WCF

Question 16: What are the possible ways of hosting a WCF service?

Answer: A WCF service can be self-hosting using a console application or Windows Forms applications. Hosting a WCF service in any managed .Net application is called self-hosting. Now the following is the procedure for creating a WCF service and hosting it in a console application. Hosting Environment Requirements:

• Availability: When do you want to be able to reach your service?
• Reliability: What happens when your service somehow breaks? How does this affect other consumers?
• Manageability: Do you need easy access to information about what is happening on the host where WCF services live?
• Versioning: Do you need to support older versions of the service? Do you know who is consuming your services?
• Deployment: What is your deployment model? Are you installing through the Microsoft Installer process and Visual Studio deployment packages, or is xcopy sufficient?
• State: Are your services stateless? Do you need sessions?

The following are the various options available for hosting a WCF Service:

1. Self-Hosting
2. Windows Service
3. Internet Information Services (IIS)
4. Windows Activation Services (WAS)

For more details visit the following link:

• Hosting WCF Service: Part 1

Question 17: What is Self Hosting in WCF?

Answer

We have our project (it may be Windows or a web application or something else) and we want to host one WCF service within this solution locally. This type of hosting is called Self-Hosting. To implement self-hosting we need to include System.Service.Model.ServiceHost namespace.

The following are the advantages of self-hosting:

• Is easy to use: With only a few lines of code you have your service running.
  
• Is flexible: You can easily control the lifetime of your services through the Open() and Close() methods of ServiceHost<T>.
  
• Is easy to debug: Debugging WCF services that are hosted in a self-hosted environment provides a familiar way of debugging, without having to attach to separate applications that activate your service.
  
• Is easy to deploy: In general, deploying simple Windows applications is as easy as xcopy. You don't need any complex deployment scenarios on server farms, and the like, to deploy a simple Windows application that serves as a WCF ServiceHost.
  
• Supports all bindings and transports: Self-hosting doesn't limit you to out-of-the-box bindings and transports whatsoever. On Windows XP and Windows Server 2003, IIS limits you to HTTP only.

The following are the disadvantages of self-hosting:

• Limited availability: The service is reachable only when the application is running.
  
• Limited features: Self-hosted applications have limited support for high availability, easy manageability, robustness, recoverability, versioning, and deployment scenarios. At least, out-of-the-box WCF doesn't provide these, so in a self-hosted scenario you have to implement these features yourself; IIS, for example, comes with several of these features by default.

For more details visit the following link:

• Understand WCF: Part 7: Self Hosting in WCF Application

Question 18: What are the main components of WCF Service?

Answer: What a Service is,

A Service is a program or application that is used by other applications. In other words, a service that is directly consumed by the end user to do their work and is something they ask for and recognize Or It's just self-contained business functionality.

What a WCF Service is

Windows Communication Foundation (WCF) was introduced in .NET 3.0. This is a great network distributed system developed by Microsoft for communication between applications. WCF is meant for designing and deploying distributed applications under a Service-Oriented Architecture (SOA) implementation. From MSDN: Windows Communication Foundation is a part of the .NET Framework that provides a unified programming model for rapidly building service-oriented applications that communicate across the web and the enterprise. WCF is a combined feature of Web Service, Remoting, MSMQ and COM+.

There are the following three main components of a WCF application.

1. WCF Service class: A WCF Service class implements some service as a set of methods.
   
2. WCF Service host: WCF supports four types of hosting, IIS, Windows Process Activation Services (WAS), self-hosting and Windows Services.
   
3. WCF Service endpoints: All communication with a Windows Communication Foundation (WCF) service occurs through the endpoints of the service. Usually the name of the Interface will be specified in the contract, so the client application will be aware of the operations that are exposed to the client.

Each endpoint contains:

• Address: An address that indicates where to find the service.
• Binding: A binding that specifies how a client can communicate with the service.
• Contract: A Contract that specifies what can the service do for us.

For more details visit the following link:

• WCF Overview

Question 19: How do we host a WCF service in IIS?

Answer 8: IIS hosting: if we are hosting a WCF Service in IIS (version 5 or 6), only the HTTP option is available as the transport protocol. In later versions of Internet Information Services (IIS), we can use any other protocol (TCP/IP, MSMQ, NamedPipes and so on.) as transport protocol.

If we host our service under IIS then we have all the features of IIS like process recycling, ideal shutdown etc. Visual Studio provides two different ways to host our WCF service in a local IIS in all are familiar with Publishing Wizard. Here we will discuss the second way using Visual Studio only in a simple manner to host our WCF service in local IIS. To host the WCF services follow the steps below.

The updated configuration for System.ServiceModel in the web.config will be as follows:

<system.serviceModel>  
    <behaviors>  
        <serviceBehaviors>  
            <behavior name=”StudentServiceBehavior”>  
                <serviceMetadata httpGetEnabled=”true”/>  
                <serviceDebug includeExceptionDetailInFaults=”false”/> </behavior>  
        </serviceBehaviors>  
    </behaviors>  
    <services>  
        <service behaviorConfiguration=”StudentServiceBehavior” name=”StudentService.StudentService”>  
            <endpoint address=”https://localhost/StudentIISHost/MyStudentHost.svc” binding=”wsHttpBinding” contract=”StudentService.IStudentService”>  
                <identity>  
                    <dns value=”localhost”/> </identity>  
            </endpoint>  
            <endpoint address=”mex” binding=”mexHttpBinding” contract=”IMetadataExchange”/> </service>  
    </services>  
</system.serviceModel>

For more details visit the following link:

• WCF Hosting in IIS Simplified

Question 20: What is one-way operation?

Answer: When an operation has no return value, and the client does not care about the success or failure of the invocation. WCF offers one-way operations to support this sort of fire-and-forget invocation,: once the client issues the call, WCF generates a request message, but no correlated reply message will ever return to the client. The one-way message exchange pattern is useful when a client needs to send information to a service but doesn't receive a response.

Use the one-way design pattern:

• When the client must call operations and is not affected by the result of the operation at the operation level.
• When using the NetMsmqBinding or the MsmqIntegrationBinding class. (For more information about this scenario, see Queues in Windows Communication Foundation.)

To create a one-way service contract, define your service contract, apply the OperationContractAttribute class to each operation, and set the IsOneWay property to true, as shown in the following sample code.

[ServiceContract(Namespace = "https://Microsoft.ServiceModel.Samples")]  
public interface IOneWayCalculator  
{  
    [OperationContract(IsOneWay = true)]  
    void Add(double n1, double n2);  
    [OperationContract(IsOneWay = true)]  
    void Subtract(double n1, double n2);  
    [OperationContract(IsOneWay = true)]  
    void Multiply(double n1, double n2);  
    [OperationContract(IsOneWay = true)]  
    void Divide(double n1, double n2);  
}

For more details visit the following link:

• One-Way Operations in WCF Services

Question 21: Why we need One Way Service?

Answer: There might be requirements where Service's Operation is not going to return any value. And at the same time client also does not bother about success or failure of service. Only for the client does calling the service matter. Client will call the operation and forget and continue with the operations.

One Way Operations

This is the way in WCF to achieve Fire and forget invocation of the service. Once the Client issues the call, WCF generates the request message and there is no corresponding response message for that. No Service side Exception will make their way to client.

Configuring One Way Operation

Boolean ISOneWay property of OperationContract class is used to configure service as one way service. We need to set this property to true. Setting true to this property turns a service operation as one way operation.

using System;  
using System.Net.Security;  
namespace System.ServiceModel  
{  
    [AttributeUsage(AttributeTargets.Method)]  
    public sealed class OperationContractAttribute: Attribute  
    {  
        public OperationContractAttribute();  
        public string Action  
        {  
            get;  
            set;  
        }  
        public bool AsyncPattern  
        {  
            get;  
            set;  
        }  
        public bool HasProtectionLevel  
        {  
            get;  
        }  
        public bool IsInitiating  
        {  
            get;  
            set;  
        }  
        public bool IsOneWay  
        {  
            get;  
            set;  
        }  
        public bool IsTerminating  
        {  
            get;  
            set;  
        }  
        public string Name  
        {  
            get;  
            set;  
        }  
        public ProtectionLevel ProtectionLevel  
        {  
            get;  
            set;  
        }  
        public string ReplyAction  
        {  
            get;  
            set;  
        }  
    }  
}

The client has nothing to do anything specific to invoke one way operation.

For more details visit the following link:

• One Way Operation in WCF

Question 22: Explain what is DataContractSerializer?

Answer: WCF provides a message-oriented programming framework. We use WCF to transmit messages between applications. Internally WCF represents all the messages by a Message class. When WCF transmits a message it takes a logical message object and encodes it into a sequence of bytes. After that WCF reads those bytes and decodes them in a logical object. The process forms a sequence of bytes into a logical object; this is called an encoding process. At runtime when WCF receives the logical message, it transforms them back into corresponding .Net objects. This process is called serialization.

WCF supports three basic serializers:

• XMLSerializer
• NetDataContractSerializer
• DataContractSerializer

WCF deserializes WCF messages into .Net objects and serializes .Net objects into WCF messages. WCF provides DataContractSerializer by default with a servicecontract. We can change this default serializer to a custom serializer like XMLSerializer.

[XmlSerializerFormat]  
[ServiceContract]  
public interface IService1  
{  
   [OperationContract]  
   void AddAuthor(Author author);  
}

The XmlSerializerFormat attribute above the ServiceContract means this serializer is for all operation contracts. You can also set a separate contract for each operation.

XMLSerializer

We can find XMLSerializer in the System.Xml.Serialization namespace. WCF supports this serialization from .Net 1.0. It is used by default with the ASP.Net webservices (ASMX).

NetDataContractSerializer

NetDataContractSerializer is analogous to .Net Remoting Formatters. It implements IFormatter and it is compatible with [Serializable] types. It is not recommended for service oriented design.

DataContractSerializer

DataContractSerializer is a default serializer for WCF. We need not to mention DataContractSerializer attribute above the service contract.

For more details visit the following link:

• WCF Serialization Part 1: Day 6

Question 23: What is Transaction Propagation? And how WCF support it?

Answer: Transaction propagation is the ability to propagate a transaction across the boundaries of a single service. Or in other words, we can say that a service can participate in a transaction that is initiated by a client.

In a SOA environment, transaction propagation becomes a key requirement. As we know, WCF supports SOA, so it provides support for transaction propagation as well.

To enable transaction propagation, we need to set the value of the TransactionFlow property of the binding being used. This can be done programmatically as follows:

WSHttpBinding bindingBeingUsed = new WSHttpBinding();  
bindingBeingUsed.TransactionFlow = "true";

Or it can be done decoratively by updating the configuration file as follows:

<bindings>  
    <wsHttpBinding>  
        <binding name="binding1" transactionFlow="true" />   
    </wsHttpBinding>  
</bindings>  

The default value for the TransactionFlow property is "False".

Do all WCF bindings support Transaction Propagation?

No. Not all WCF bindings support transaction propagation. Only the following list of bindings support it:

• wsHttpBinding
• netTcpBinding
• netNamedPipeBinding
• wsDualHttpBinding
• wsFederationHttpBinding

For more details visit the following link:

• WCF Service FAQs - Part 4

Question 24: What is WCF throttling?

Answer 14: WCF throttling provides some properties that you can use to limit how many instances or sessions are created at the application level. Performance of the WCF service can be improved by creating proper instance.

The throttling of services is another key element for WCF performance tuning. WCF throttling provides the prosperities maxConcurrentCalls, maxConcurrentInstances, and maxConcurrentSessions, that can help us to limit the number of instances or sessions are created at the application level.