WCF Contracts

 Contract  : Contracts are  standard way of describing what the service does . Contract should be an Interface or class but for best practice use interface.

<endpoint  address="http://localhost:8080/MyService/MyService.svc" binding="wsHttpBinding" contract="MyInterface">

Types of Contracts

• Service Contracts
• Data Contracts      
• Fault Contracts   
• Message Contracts

Service Contracts :  

Describe which operations the client can perform on the service. A Service can have more than one service contract but it should have at least one Service contract.

There are two types of Service Contracts. 

• ServiceContract - This attribute is used to define the Interface.
• OperationContract - This attribute is used to define the method inside Interface. 

[ServiceContract]

interface  IMyContract

{

   [OperationContract]

   string MyMethod( );

}

class MyService : IMyContract

{

   public string MyMethod( )

   {

      return "First Service contract";

   }

}

Data Contract

Datacontract is used to communicate between client and server or formal agreement between a service and a client that abstractly describes the data to be exchanged.

Implicit =  Simple type such as int, string etc has an implicit data contract. 

Explicit =  User defined object are,  for which you have to define a Data contract using [DataContract] and [DataMember] attribute.

[DataContract]

public class Person

{

    [DataMember]

    public string name;

}

[DataContract]

public class Employee : Person

{

    [DataMember]

    public int department;

    [DataMember]

    public string title;

    [DataMember]

    public int salary;

}

Fault Contract  :

 This error should be reported to the client in proper manner. Basically when we develop managed application or service, we will handle the exception using try- catch block. But these exceptions handlings are technology specific.

 

[ServiceContract]

interface  IMyContract

{

   [OperationContract]

   [FaultContract(typeof(MyFaultException))]

   string MyMethod( );

}

class MyService : IMyContract

{

   public string MyMethod( )

   {

      return "First Service contract";

   }

}

Message Contract

Sometimes you complete control over the structure of a SOAP message  is just as important as control over its contents then you can user message contracts both header and body content.. Message is the packet of data which contains important information. WCF uses these messages to transfer information from Source to destination. WCF uses SOAP (Simple Object Access Protocol) Message format for communication.

Simplex - It is one way communication. Source will send message to target, but target will not respond to the message. Request/Replay - It is two way communications, when source send message to the target, it will resend response message to the source. But at a time only one can send a message Duplex - It is two way communication, both source and target can send and receive message simultaniouly.

[MessageContract]
    public class DownlaodStreamItem
    {

        [MessageHeader]
        public Int64 ItemID { set; get; }

        [MessageHeader]
        public Int64 SizeOfFile { set; get; }

        [MessageHeader]
        public String Word { set; get; }

        [MessageBodyMember]
        public Stream Data { set; get; }
    }