Question

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

Answer 1

MEP stands for Message Exchange Pattern. In WCF we are creating services. What does a service do for us? A service does some task on behalf of us or sends a response back from our request. All such communications are done using messages. We send some message as a request and get a message as a response from the service. WCF supports three types of MEPs:

• Request / Response
• One-Way
• Duplex

Message Exchange Patterns describes the way of communication between Client and Server means how client and server would be exchange messages to each other. There are three types of message exchange patterns.

Request/Response

Request / Response is a very common MEP. To set this pattern we need to set the IsOneWay property of OperationContractAttribute as false. And the default value of the IsOneWay property is false. So ultimately we do not need to set this property. It is set by default. That is why it is very easy to implement.

1. [ServiceContract]  
2. publicvinterface RequestReplyService  
3. {   
4.    [OperationContract]  
5.    string GetData(int value);  
6.   
7.    [OperationContract(IsOneWay = false)]  
8.    voidSaveData(string value);  
9. }  

One-Way:

Set the IsOneWay property of OperationContractAttribute to true for a OneWay message exchange pattern. Suppose you send a message to a service. This pattern is used when the service does some operation and you do not want a response back. For example you want to change the status of a transaction from pending to completed and you do not want to get a confirmation from the service that the status is changed. You can use a OneWay pattern.

1. [ServiceContract]  
2. public interface IService1  
3. {  
4.    [OperationContract(IsOneWay=true)]  
5.    void ChangeTransactionStatus(int value);  
6. }  

Duplex:

The duplex MEP is a two-way message channel. When the client sends a message to the service to instantiate some long-running processing and requires notification back from the service, a duplex MEP is applicable.

There are two types of contacts, ServiceContract and CallbackContract required to implement a duplex MEP. This MEP is declared by associating a CallbackContract with the ServiceContract. It is done through a CallbackContract property of ServiceContract.