Hosting the Data Service (WCF Data Services)
By using WCF Data Services, you can create a service that exposes data as an Open Data Protocol (OData) feed. This data service is defined as a class that inherits from DataService<T>. This class provides the functionality required to process request messages, perform updates against the data source, and generate responses messages, as required by OData. However, a data service cannot bind to and listen on a network socket for incoming HTTP requests. For this required functionality, the data service relies on a hosting component.
The data service host performs the following tasks on behalf of the data service:
Listens for requests and routes these requests to the data service.
Creates an instance of the data service for each request.
Requests that the data service process the incoming request.
Sends the response on behalf of the data service.
To simplify hosting a data service, WCF Data Services is designed to integrate with Windows Communication Foundation (WCF). The data service provides a default WCF implementation that serves as the data service host in an ASP.NET application. Therefore, you can host a data service in one of the following ways:
In an ASP.NET application.
In a managed application that supports self-hosted WCF services.
In some other custom data service host.
When you use the Add New Item dialog in Visual Studio to define a data service in an ASP.NET application, the tool generates two new files in the project. The first file has a .svc extension and instructs the WCF runtime how to instantiate the data service. The following is an example of this file for the Northwind sample data service created when you complete the quickstart:
<%@ ServiceHost Language="C#" Factory="System.Data.Services.DataServiceHostFactory, System.Data.Services, Version=220.127.116.11, Culture=neutral, PublicKeyToken=b77a5c561934e089" Service="NorthwindService.Northwind" %>
This directive tells the application to create the service host for the named data service class by using the DataServiceHostFactory class.
The code-behind page for the .svc file contains the class that is the implementation of the data service itself, which is defined as follows for the Northwind sample data service:
Because a data service behaves like a WCF service, the data service integrates with ASP.NET and follows the WCF Web programming model. For more information, see WCF Services and ASP.NET and Web Programming Model.
Because it incorporates a WCF implementation, WCF Data Services support self-hosting a data service as a WCF service. A service can be self-hosted in any .NET Framework application, such as a console application. The DataServiceHost class, which inherits from WebServiceHost, is used to instantiate the data service at a specific address.
Self-hosting can be used for development and testing because it can make it easier to deploy and troubleshoot the service. However, this kind of hosting does not provide the advanced hosting and management features provided by ASP.NET or by Internet Information Services (IIS). For more information, see Hosting in a Managed Application.
For cases where the WCF host implementation is too restrictive, you can also define a custom host for a data service. Any class that implements IDataServiceHost interface can be used as the network host for a data service. A custom host must implement the IDataServiceHost interface and be able to handle the following basic responsibilities of the data service host:
Provide the data service with the service root path.
Process request and response headers information to the appropriate IDataServiceHost member implementation.
Handle exceptions raised by the data service.
Validate parameters in the query string.