vb.net qr code dll Running the Application in Visual Basic .NET

Draw Data Matrix ECC200 in Visual Basic .NET Running the Application

Now you re ready to run the application. Other than the 20-second delay when you assign an agent, it should work just like the solution from 13. You can demonstrate that both updates are committed as an atomic unit by closing the application after you click the Assign button. The Lead record is updated before the delay, but not committed until after the delay. If you close the application during the delay, this update should be rolled back. Look at the data in the Lead table and verify that the Status is still Open and the AssignedTo field is null. If you restart the application, you should be able to select this lead and assign an agent.

Caution When a workflow instance is created or loaded from the persistence store, it is locked to prevent other users from accessing it. Under normal circumstances, it is unlocked when the instance becomes idle (and is unloaded from memory). If you close the application when an activity is in progress, the normal unlock sequence is skipped. When you shut down the application and restart it, it might look like a different user to the workflow and when you try to reload it, you ll get an InstanceLockedException. The instance store will eventually release the lock; you might have to wait a minute or so.

In this chapter, you will modify the application to coordinate the database updates with the workflow persistence so they are performed on the same database transaction. This will ensure that your application tables are consistent with the instance data. You will provide extensions that override the PersistenceParticipant class and update your application data when the workflow is persisted.

You will reuse the project that you developed in 14. Start by creating a blank solution, as shown in Figure 15-1. For the solution name, enter 15.

From Windows Explorer, copy the LeadGenerator folder from the 14 folder to the 15 folder. Back in Visual Studio, from the Solution Explorer, right-click the 15 solution and choose Add Existing Project. Select the LeadGenerator project that you just copied to the 15 folder. Create a 15 database and run the following scripts to initialize the database schema: SqlWorkflowInstanceStoreSchema.sql SqlWorkflowInstanceStoreLogic.sql Lead.sql Tracking.sql

In 12, you created a CommentExtension that allowed you to append a comment string. The comment was persisted along with the workflow instance data by inheriting from the PersistenceParticipant class and overriding the CollectValues() and PublishValues() methods. You will now use a similar approach in this chapter, but first, let s review. Persistence providers perform two basic operations: Save when a workflow instance is persisted to a durable store Load when a workflow instance is reloaded into memory

When one of these operations is being performed, the extensions included on the instance are enumerated. The corresponding methods are called in any extension that is derived from the PersistenceParticipant class. The CollectValues() method in the CommentExtension returned the comment string to the persistence provider. This was then passed back to the CommentExtension when the PublishValues() method was called. Although this is a convenient way to persist custom data, the data is persisted as part of the workflow state data. Now I ll show you how this technique can be used to update application tables (such as the Lead and Assignment tables you re using).

You will create a custom extension that will perform updates to the Lead table when the workflow is persisted. From the Solution Explorer, right-click the Extensions folder (under the LeadGenerator project) and choose Add Class. For the class name, enter PersistLead.cs. The implementation of this class is shown in Listing 15-1.