WCF Overview

WCF is a .NET platform for developing services .Service is any functionality that can be consumed by the outside world. A service defines well defined communication protocols to communicate with it.

A service can be located anywhere , it could be on local machine on the intranet or even internet.A client consumes the functionality exposed by the service.A service can be anything it can be an independent application like asp.net or it can be another service.

Client and Service communicate with each other by sending messages.

SOAP Message SOAP Message

Client HTTP/TCP /MSMQ HTTP/TCP/MSMQ Server



Figure: Basic Client Server Communication

Since the functionality of the service is hidden to the outside world. Service exposes metadata that client uses to communicate with the service. Metadata can be in any technology neutral format like wsdl.

Client always uses proxy to communicate with the service irrespective of where service is located. In WCF every service has endpoints and the client uses theses endpoints to communicate with the service.

Every endpoint has three important pieces of information.

Address , Binding and Contract.

Address specifies the location of the service.

Binding specifies how to communicate with the service(protocol).

Contract specifies what the service does.

A typical endpoint in the configuration file appears as :

<endpoint address = "http://localhost/TestService/" binding="wsHttpBinding"
contract = "MyNamespace.IContract"/>

WCF has mainly following types of contracts

1. Service Contract: Describes the operations of the services
2. Operation Contract: Describes the operations available on the service
   
3. Data Contract: Define the data types passed to and from the service
   
4. Fault Contract: Define the erros raised by the service
   
5. Message Contract: Allows the service to interact directly by using the message.
   

Basic WCF service

System.ServiceModel.dll is the main assembly for WCF services. To create a WCF service we need to apply the service contract attribute either on the interface or the class.

namespace WcfService1
{

     [ServiceContract]
    public interface IService1
    {

        [OperationContract]
        string HelloWorld();

    }

    public class Service1 : IService1
    {      
          public string HelloWorld()
            {
                return "Hello WCF";
            }

      }
}

We can also use explicit interface implementation like this :

         string IService1.HelloWorld()
            {
                return "Hello WCF";
            }

Note when using explicit interface implementation we can't use the public access modifier.

Method Overloading

To use method overloading we need to use the name attribute of the OperationContract attribute.

If we write the following implementation for method overloading it will throw an exception at service host load time.

        [OperationContract]
        string HelloWorld();
 
        [OperationContract]
        string HelloWorld(string Message);

To use method overloading in WCF service we need to use the Name attribute of the OperationContract attribute.

        [OperationContract(Name="HelloWorld")]
        string HelloWorld();
 
        [OperationContract(Name = "HellowWorldMssg")]
        string HelloWorld(string Message);

In the later articles we will see how to host the service and call it using the client application.

Data Contracts

We can pass only the primitive datatypes to OperationContracts .If we want to pass custom data types to OperationContracts we need to use the DataContract Attribute on the Custom datatype.

    [DataContract]
    class Customer
    {
        int name;

        [DataMember]
        public int Name
        {
            get { return name; }
            set { name = value; }
        }
        int address;

        [DataMember]
        public int Address
        {
            get { return address; }
            set { address = value; }
        }

    }