Loading and Unloading Instances in Visual C#

Printer UPC Code in Visual C# Loading and Unloading Instances

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12. Of course, the application isn t waiting for workflow completion since no workflow was started. To create a workflow instance, add this code following the line of code you just located:

// Create the workflow instance. WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(IdledWorkflow.Workflow1)); // Start the workflow instance. instance.Start();

13. Compile the solution by pressing F6. Correct any compilation errors that pop up. Now, when you execute the WorkflowIdler application, the Delay Activity will force the workflow instance to be persisted to the storage database. However, you might wait longer than 30 seconds (up to 2 minutes) for the instance to be reloaded. That s because the workflow runtime periodically checks for persisted workflows in idle states due to delays, but it is not guaranteed that those workflows will wait only for their respective delays. WF polls the database periodically, looking for idled workflows that were persisted waiting for timer events (Delay Activity uses a timer). The default polling time is 2 minutes. Note The default database polling time can be changed by providing a TimeSpan to the SqlWorkflowPersistenceService and using the constructor that takes four parameters (the connection string, the unload on idle flag, a TimeSpan indicating how long the current instance of the persistence service owns this instance of the workflow, and a TimeSpan indicating how often the database should be polled). If you want to continue to the next chapter, keep Visual Studio 2005 running, and turn to 7, Basic Activity Operations. We ll start digging into some of the activities WF provides us with. If you want to stop, exit Visual Studio 2005 now, save your spot in the book, and close it. Just don t forget all those persisted workflows in your database!

To Create the workflow persistence database Do This After creating a new database for the task, execute within SQL Server Management Studio Express the SQL scripts you find in the <%WINDIR%>\Microsoft.NET\Framework\v3.0\Windows Workflow Foundation\SQL\EN directory within SQL Server Management Studio. You ll need to execute both the SqlWorkflowPersistenceService_Schema.sql script and the SqlWorkflowPersistenceService_Logic.sql script.

Introducing Windows Workflow Foundation (WF)

Do This After creating an instance of WorkflowRuntime but before you call its StartRuntime method, add a new instance of SqlWorkflowPersistenceService to the runtime services using WorkflowRuntime.AddService. Call WorkflowInstance.Unload or WorkflowInstance.TryUnload. Keep in mind that the Unload is synchronous and will block your thread until the unload operation is complete or throws an exception. Call WorkflowInstance.Load. Introduce a Delay activity to your workflow processing and start SqlWorkflowPersistenceService with the UnloadOnIdle flag set. When the Delay activity begins execution, the workflow instance enters the idle state. At that point, SqlWorkflowPersistenceService automatically unloads your workflow and serializes it to the database. Later, after the delay period has expired, the instance will be reloaded and re-executed.

Manually load a previously persisted workflow instance Automatically unload, persist, and reload a workflow instance

In this part: 7: Basic Activity Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 8: Calling External Methods and Workflows . . . . . . . . . . . . . . . . 151 9: Logic Flow Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 10: Event Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 11: Parallel Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 12: Policy and Rules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 13: Crafting Custom Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295