What are Contracts in WCF?

Contract provides Interoperability to communicate with the client. It is a type of contract between client and service.

In WCF, we have the following types of contract.

Service Contract
Operation Contract
Data Contract
Message Contract
Fault Contract

Service Contract: A service contract defines the operations which are exposed by the service to the outside world. Here's an example.

[ServiceContract]
interface IEmployee
{
[OperationContract]
EmployeeDetail GetEmployee(EmployeeInfo emp);
}

Operation Contract: We define Operation Contract inside Service Contract.

[ServiceContract]
interface IEmployee
{
[OperationContract]
EmployeeDetail GetEmployee(EmployeeInfo emp);
}

Data Contract: Data Contract describes the Data to be exchanged.

[DataContract]
public class EmployeeInfo
{
}

Message Contract: Message Contract gives more control over the actual SOAP message for a service operation request or reply. A message contract defines the elements of a message (like Message Header, Message Body, etc), as well as the message-related settings, such as the level of message security.

[ServiceContract]
public interface IEmployeeService
{
[OperationContract]
EmployeeDetail CalPrice(Employee request);
}
[MessageContract]
public class Employee
{
[MessageHeader]
public MyHeader SoapHeader
{
get;
set;
}
[MessageBodyMember]
public EmployeeInfo Employee
{
get;
set;
}
}
[DataContract]
public class MyHeader
{
[DataMember]
public string EmpID
{
get;
set;
}
}
[DataContract]
public class EmployeeInfo
{
[DataMember]
public string EMP_Name
{
get;
set;
}
[DataMember]
public sring Country
{
get;
set;
}
[DataMember]
public string City
{
get;
set;
}
[DataMember]
public string Mobile {
get;
set;
}
}

Fault Contract: Fault Contract defines the errors raised by the service.

[ServiceContract]
interface IEmpContract
{
[FaultContract(typeof(MyFaultContract1))]
[FaultContract(typeof(MyFaultContract2))]
[OperationContract]
string GetEmployeeAddress();
[OperationContract]
string ShowEmployee();
}