Windows Communication Foundation Services and WCF Data Services in Visual Studio

Windows Communication Foundation Services and WCF Data Services in Visual Studio

Visual Studio 2008 provides tools for working with Windows Communication Foundation (WCF) and WCF Data Services, Microsoft technologies for creating distributed applications. This topic provides an introduction to services from a Visual Studio perspective.

What Is WCF?

Windows Communication Foundation (WCF) is a unified framework for creating secure, reliable, transacted, and interoperable distributed applications. In earlier versions of Visual Studio, there were several technologies that could be used for communicating between applications.

If you wanted to share information in a way that enabled it to be accessed from any platform, you would use a Web service (also known as an ASMX Web service). If you wanted to just move data between a client and server that was running on the Windows operating system, you would use .NET Remoting. If you wanted transacted communications, you would use Enterprise Services (DCOM), or if you wanted a queued model you would use Message Queuing (also known as MSMQ).

WCF brings together the functionality of all those technologies under a unified programming model. This simplifies the experience of developing distributed applications.

What are WCF Data Services

WCF Data Services are services that interact directly with a database, allowing you to return data using standard HTTP verbs such as GET, POST, PUT or DELETE. In general, WCF Data Services are a good choice for applications that are used to create, update, or delete records in a database. For more information, see ADO.NET Data Services Framework.

WCF Programming Model

The WCF Programming model is based on communication between two entities: a WCF service and a WCF client. The programming model is encapsulated in the System.ServiceModel namespace in the .NET Framework.

WCF Service

A WCF service is based on an interface that defines a contract between the service and the client. It is marked with a ServiceContractAttribute attribute, as shown in the following code:

C#

 [ServiceContract]

public interface IService1

C#

 [OperationContract]

string GetData(string value);

You define functions or methods that are exposed by a WCF service by marking them with a OperationContractAttribute attribute. In addition, you can expose serialized data by marking a composite type with a DataContractAttribute attribute. This enables data binding in a client.

After an interface and its methods are defined, they are encapsulated in a class that implements the interface. A single WCF service class can implement multiple service contracts.

A WCF service is exposed for consumption through what is known as an endpoint. The endpoint provides the only way to communicate with the service; you cannot access the service through a direct reference as you would with other classes.

An endpoint consists of an address, a binding, and a contract. The address defines where the service is located; this could be a URL, an FTP address, or a network or local path. A binding defines the way that you communicate with the service. WCF bindings provide a versatile model for specifying a protocol such as HTTP or FTP, a security mechanism such as Windows Authentication or user names and passwords, and much more. A contract includes the operations that are exposed by the WCF service class.

Multiple endpoints can be exposed for a single WCF service. This enables different clients to communicate with the same service in different ways. For example, a banking service might provide one endpoint for employees and another for external customers, each using a different address, binding, and/or contract.

WCF Client

A WCF client consists of a proxy that enables an application to communicate with a WCF service, and an endpoint that matches an endpoint defined for the service. The proxy is generated on the client side in the app.config file and includes information about the types and methods that are exposed by the service. For services that expose multiple endpoints, the client can select the one that best fits its needs, for example, to communicate over HTTP and use Windows Authentication.

After a WCF client has been created, you reference the service in your code just as you would any other object. For example, to call the GetData method shown earlier, you would write code that resembles the following:

C#

private void button1_Click(System.Object sender, System.EventArgs e)

{

    ServiceReference1.Service1Client client = new

        ServiceReference1.Service1Client();

    string returnString;

    returnString = client.GetData(textBox1.Text);

    label1.Text = returnString;

}