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Consuming Services
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The Add Service Reference dialog box
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The Service Reference Settings dialog box for adding a service reference
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Visual Studio uses the same svcutil tool, but it provides you with a friendly interface and takes care of some of the manual steps you need to perform when using svcutil yourself, such as adding the reference to System.ServiceModel, adding the resulting proxy code to your project, and so on.
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Lesson 1: Consuming WCF Services
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Visual Studio Service Reference vs. svcutil
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Which one is the better approach: using Visual Studio or svcutil to create your proxy classes In many cases, it s a matter of developer preference, but here are a few points to consider: Using the svcutil utility gives you the most control. Using the svcutil utility requires additional manual steps such as adding the reference to System.ServiceModel, adding the resulting proxy code to your project, and so on, that Visual Studio does automatically. The svcutil utility can be useful in an automated build scenario in which you want to generate proxy classes as part of the automated build process.
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Manually Defining a Proxy Class
As opposed to having a tool generate a proxy class for you, you can manually define a proxy class on your own using the same base classes that the tools use. Suppose you have the following Service contract:
' VB <ServiceContract()> _ Public Interface IOrderEntryService <OperationContract()> _ Function SubmitOrder(ByVal order As Order) _ As OrderAcknowledgement ' Etc... End Interface // C# [ServiceContract()] public interface IOrderEntryService { [OperationContract()] OrderAcknowledgement SumbitOrder(Order order); // Etc... }
You could manually define a proxy class based on that contract as follows:
' VB Public Class OrderEntryServiceProxy Inherits ClientBase(Of IOrderEntryService) Implements IOrderEntryService Public Sub New(ByVal binding As Binding, _ ByVal epAddr As EndpointAddress)
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Consuming Services
MyBase.New(binding, epAddr) End Sub Public Sub New(ByVal endpointConfigurationName As String) MyBase.New(endpointConfigurationName) End Sub Public Function SubmitOrder(ByVal order As Order) _ As OrderAcknowledgement _ Implements IOrderEntryService.SubmitOrder Return Me.Channel.SubmitOrder(order) End Function End Class // C# public class OrderEntryServiceProxy : ClientBase<IOrderEntryService>,IOrderEntryService { public OrderEntryServiceProxy( Binding binding, EndpointAddress epAddr) : base(binding,epAddr) { } public OrderEntryServiceProxy( string endpointConfigurationName) : base(endpointConfigurationName) { } public OrderAcknowledgement SumbitOrder(Order order) { return this.Channel.SumbitOrder(order); } }
If a callback channel is involved (perhaps the Service contract specifies a Callback contract because at least one of the service operations uses the Duplex message exchange pattern [MEP]), the base class should be DuplexClientBase instead of ClientBase. There are more steps to setting up a callback channel, as is explained later in this lesson and in the lab that follows.
Dynamically Creating a Proxy
In some cases, you don t need to have a proxy class explicitly defined anywhere because WCF provides the ChannelFactory class as a means of dynamically creating a proxy object based on the Service contract alone. Without ever explicitly generating a proxy class or manually defining one, you can create a proxy object, using only the Service contract and the ChannelFactory class. The following code shows how this would be done.
Lesson 1: Consuming WCF Services
' VB Dim binding As Binding binding = New NetTcpBinding Dim factory As ChannelFactory(Of IOrderEntryService) factory = New ChannelFactory(Of IOrderEntryService)( _ binding, "net.tcp://localhost:6789/orders/") Dim proxy As IOrderEntryService proxy = factory.CreateChannel() Try Dim order As New Order order.Product = "Widget-ABC" order.Quantity = 10 ' Etc... Dim ack As OrderAcknowledgement ack = proxy.SubmitOrder(order) Console.WriteLine( _ "Order submitted; tracking number: {0}", _ ack.TrackingNumber) Catch ex As Exception Console.WriteLine("Error: {0}", ex.Message) End Try // C# Binding binding = new NetTcpBinding(); ChannelFactory<IOrderEntryService> factory; factory = new ChannelFactory<IOrderEntryService>( binding, "net.tcp://localhost:6789/orders/"); try { IOrderEntryService proxy = factory.CreateChannel(); Order order = new Order(); order.Product = "Widget-ABC"; order.Quantity = 10; // Etc... OrderAcknowledgement ack = proxy.SumbitOrder(order); Console.WriteLine( "Order submitted; tracking number: {0}", ack.TrackingNumber); } catch (Exception ex) { Console.WriteLine("Error: {0}",ex.Message); }
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Consuming Services
BEST PRACTICES
Generate proxy classes from service metadata
One of the tenets of service orientation is that consumers should depend only on a service s schema and not on any of the service s classes. The only way consumers of a service should be coupled to the service is through the schema of the messages they must exchange with the service. That is certainly better than some of the middleware technologies of the past such as DCOM, CORBA, and .NET Remoting, which required consumers to have a code or binary-level dependency on the service and the request and response objects. If you manually create proxy classes or use the ChannelFactory class to create proxy objects dynamically, you need to have access to the WCF Service contract. If you are not getting access to the service contract by generating code from service metadata, that means you must have a code or binary-level reference to the WCF Service contract. Avoid that form of coupling when building services. Always strive to minimize the coupling between a service and its consumers. In short, always generate proxy classes from service metadata, either by using svcutil or by adding a service reference in Visual Studio.
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