In WCF, all services expose contracts. The contract is a platform-neutral and standard way of describing what the service does.

WCF defines four types of contracts.

Service contracts:

Describe which operations the client can perform on the service. 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 "Hello World";

}

}

Data contracts:

Define which data types are passed to and from the service. WCF defines implicit contracts for built-in types such as int and string, but we can easily define explicit opt-in data contracts for custom types.

There are two types of Data Contracts.

DataContract - attribute used to define the class

DataMember - attribute used to define the properties.

[DataContract]

class Contact

{

[DataMember]

public string FirstName;

[DataMember]

public string LastName;

}

If DataMember attributes are not specified for a properties in the class, that property can't be passed to-from web service.

Fault contracts:

Define which errors are raised by the service, and how the service handles and propagates errors to its clients.