WCF Service Contracts And Operation Contracts

Here, we will learn about Service Contracts and Operation Contracts in WCF.

Basically a WCF Contract is an agreement between the two parties, in other words a Service and a Client. In Windows Communication Foundation, contracts can be categorized as behavioral or structural.
 

Behavioral Contracts

  • The ServiceContract attribute marks a type as a Service Contract that contains operations.
  • OperationContract attribute marks the operations that will be exposed.
  • FaultContract defines what errors are raised by the service being exposed.

Structural Contracts

  • The DataContract attribute defines the types that will be moved between the parties.
  • The MessageContract attribute defines the structure of the SOAP message.
In this WCF Tutorial, we will discuss and implement contracts in Windows Communication Foundation using a step-by-step approach with practical examples.
 

Service Contract and Operation Contract

 
A Service Contract basically describes the operations a service exposes to another party (in other words a client). We can map a WCF Service Contract to a Web Service Description Language (WSDL).
 
It's recommended to apply the ServiceContract attribute to an interface, although it can be applied to a class as well. Applying it to an interface provides us a clear separation of contract and its implementation.
 
Service Contract  
 
It describes:
  • What operations are exposed by the service
  • Platform independent description of the interface as well as methods of our service
  • A Message Exchange Pattern (MEP) between the parties, in other words Request/Response, One-Way or Duplex. Please follow here for a detailed description of MEPs.
To define a Service Contract, we will apply the ServiceContract attribute to a .NET Interface and OperationContract attribute to methods as follows:
  1. [ServiceContract]  
  2. interface ISimpleService  
  3. {  
  4.      [OperationContract]  
  5.      string SimpleOperation();  
  6. }  
  7. class SimpleService  :  ISimpleService  
  8. {  
  9.        public string SimpleOperation()  
  10.        {  
  11.             return "Simple Operation Result";  
  12.         }  
  13. }  
In the code above, we used the ServiceContract attribute to mark ISimpleService (an interface) as a Service Contract and the OperationContract attribute to the method "SimpleOperation". Also provided an implementation class "SimpleService".
 
Note: The ServiceContract attribute is not inherited, in other words if we are defining another interface/class as a Service Contract inheriting from ISimpleContract, we still need to explicitly mark it with the ServiceContract attribute.
 
In the preceding example, we use a ServiceContract attribute without any parameter but we can pass parameters also like Name, Namespace, ConfigurationName, ProtectionLevel, SessionMode and so on as follows:
  1. [ServiceContract(Name = "MySimpleService")]  
  2. interface ISimpleService  
  3. {  
  4.     [OperationContract]  
  5.     string SimpleOperation();  
  6. }