Calling a WCF Ser vice from WF in .NET framework

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Calling a WCF Ser vice from WF
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property; a eld is local to the work ow class, whereas a property has broader visibility within the WF design environment
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Figure 113 Proxy type was imported so an operation can be chosen
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Property or Field
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A property is a eld that can be initialized when a work ow instance is started You can send a value into the work ow on startup by de ning a dictionary object and passing it as the optional second parame If you de ne a property, the ter of value passed into the work ow can be passed along to subsequent services or other activities invoked from the work ow
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Figure 114 shows the WF variable, , operation bound to the return value from the Finally, you must con gure the service endpoint properties so that the Send activity formats and sends the message to the right location This is
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11: Workflow Ser vice s
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done by con guring the property, which has three components: , , and The indicates the scope of the and is selected from a must match an endpoint con guradrop-down list box The such as one that was generated from Add Service tion name in Reference or
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Figure 114 Binding WF variable to service operation parameters
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Writing a Custom Activity Custom activities in WF are a great way to encapsulate business capabilities By providing the right level of abstraction and granularity in custom activities, a WF developer can model an application by combining those capabilities Although using the Send activity is a great method for calling any interoperable Web service, it requires the WF developer to know that the business capability they want to consume is, in fact, a Web service Custom activities encapsulate that knowledge so the WF developer can model the application, not the plumbing In the simplest case, a custom activity is a NET class that derives from There are many subclasses that derive from this, to specialize for sequential or state-machine models,
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Calling a WCF Ser vice from WF
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or composite activities Only one method in that class, , is required method is an The return value from the enumeration If set to , the activity is done If not, WF manages the activity instance until the activity noti es the WF runtime that it is complete Custom activities can expose properties to the WF designer at runtime Properties can be set in Visual Studio at design time and can be bound to WF variables that are available at runtime The properties are, in effect, the method on the custom activity interface to the custom activity The only requires context as a parameter, because the interface is done through properties To create a custom activity, you can use the Work ow Activity Library template in Visual Studio 2008 The template creates a custom activtype, which derives from ity of Listing 112 shows a custom activity Note that other than the construc This method is where you insert tor, there is only one method, code to call the WCF service In this example, we create the proxy and call the method off the proxy When the proxy is generated, WCF creates an appcon g le in the local project At runtime, when the activity is called, WCF will look in the current application con guration le for service model information Therefore, the service model con guration must be le used for the work ow host copied into the and price Both are visible There are two properties de ned, from the Visual Studio design surface and from code at runtime
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Listing 112 Implementing a Custom WF Activity
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11: Workflow Ser vice s
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Listing 112 continued
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After creating the activity library, the activity can be used in a work ow project The work ow is unaware the WCF is involved, because that
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plumbing is encapsulated in the custom activity Figure 115 shows a workcustom activity ow using the
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Figure 115 Using a custom activity in a workflow
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Exposing a Service from WF
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Developers typically use WF for building reactive programs The program starts, does something useful, waits for input, does something else useful, waits for more input, and so on At some deterministic point, the work ow program ends Reactive programs may run for a very long time, during which the client or server computer may be shut down There also may be many copies of the work ow instances running simultaneously, and each instance must be uniquely addressable so it can receive external input Although these qualities are not unique to WF, they do require special attention The WF design and runtime environment taps into WCF extensibility points to support these key requirements It handles long-running work ows that persist across system failure It correlates incoming messages to existing work ows so that a scalable host can support many running