Domain Service

     Domain services are WCF services that expose the business logic of a WCF RIA Services application. Domain service contains set of business related data operation and it is exposed as WCF service. 

Domain Context class at the client side is used to consume the Domain service by using Domain Client object. it is available inside the namespace  "System.ServiceModel.DomainServices.Client"

Below diagram explains integration of the RIA service with WCF.
   

The Domain Service class is the base class for all classes that serve as domain services.

• DomainServiceHost is the hosting class for domain service; internally
• DomainServiceHost uses the WCF Service Host class to host the application.

A domain service class must be marked with the EnableClientAccessAttribute attribute to make the service available to the client project. The EnableClientAccessAttribute is automatically applied to a domain service when you select the Enable client access check box in the Add New Domain Service Class dialog box. When the EnableClientAccessAttribute attribute is applied to a domain service, RIA Services generates the corresponding classes for the client project.

Example:

 [EnableClientAccess()]

    Public class EmployeeDomainService: DomainService

    {

        Private EmployeeData data = EmployeeData.Instance;

        Public IEnumerable < Employee> GetEmployees ()

        {

            Return data.EmployeeList;

        }

    }