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Flowing Transactions into and out of Workflow Services

  • Artikkeli

Workflow services and clients can participate in transactions. For a service operation to become part of an ambient transaction, place a Receive activity within a TransactedReceiveScope activity. Any calls made by a Send or a SendReply activity within the TransactedReceiveScope will also be made within the ambient transaction. A workflow client application can create an ambient transaction by using the TransactionScope activity and call service operations using the ambient transaction. This topic walks you through creating a workflow service and workflow client that participate in transactions.

Warning

If a workflow service instance is loaded within a transaction and the workflow contains a Persist activity, the workflow instance will block until the transaction times out.

Important

Whenever you use a TransactedReceiveScope it is recommended to place all Receives in the workflow within TransactedReceiveScope activities.

Important

When using TransactedReceiveScope and messages arrive in the incorrect order, the workflow will be aborted when trying to deliver the first out of order message. You must make sure your workflow is always at a consistent stopping point when the workflow idles. This will allow you to restart the workflow from a previous persistence point should the workflow be aborted.

Create a shared library

  1. Create a new empty Visual Studio Solution.

  2. Add a new class library project called Common. Add references to the following assemblies:

    • System.Activities.dll

    • System.ServiceModel.dll

    • System.ServiceModel.Activities.dll

    • System.Transactions.dll

  3. Add a new class called PrintTransactionInfo to the Common project. This class is derived from NativeActivity and overloads the Execute method.

    using System;  
using System;  
using System.Activities;  
using System.Transactions;  

namespace Common  
{  
    public class PrintTransactionInfo : NativeActivity  
    {  
        protected override void Execute(NativeActivityContext context)  
        {  
            RuntimeTransactionHandle rth = context.Properties.Find(typeof(RuntimeTransactionHandle).FullName) as RuntimeTransactionHandle;  

            if (rth == null)  
            {  
                Console.WriteLine("There is no ambient RuntimeTransactionHandle");  
            }  

            Transaction t = rth.GetCurrentTransaction(context);  

            if (t == null)  
            {  
                Console.WriteLine("There is no ambient transaction");  
            }  
            else  
            {  
                Console.WriteLine("Transaction: {0} is {1}", t.TransactionInformation.DistributedIdentifier, t.TransactionInformation.Status);  
            }  
        }  
    }  

}

    This is a native activity that displays information about the ambient transaction and is used in both the service and client workflows used in this topic. Build the solution to make this activity available in the Common section of the Toolbox.

Implement the workflow service

  1. Add a new WCF Workflow Service, called WorkflowService to the Common project. To do this right click the Common project, select Add, New Item ..., Select Workflow under Installed Templates and select WCF Workflow Service.

    Adding a Workflow Service

  2. Delete the default ReceiveRequest and SendResponse activities.

  3. Drag and drop a WriteLine activity into the Sequential Service activity. Set the text property to "Workflow Service starting ..." as shown in the following example.

    ![Adding a WriteLine activity to the Sequential Service activity(./media/flowing-transactions-into-and-out-of-workflow-services/add-writeline-sequential-service.jpg)

  4. Drag and drop a TransactedReceiveScope after the WriteLine activity. The TransactedReceiveScope activity can be found in the Messaging section of the Toolbox. The TransactedReceiveScope activity is composed of two sections Request and Body. The Request section contains the Receive activity. The Body section contains the activities to execute within a transaction after a message has been received.

    Adding a TransactedReceiveScope activity

  5. Select the TransactedReceiveScope activity and click the Variables button. Add the following variables.

    Adding variables to the TransactedReceiveScope

    Note

    You can delete the data variable that is there by default. You can also use the existing handle variable.

  6. Drag and drop a Receive activity within the Request section of the TransactedReceiveScope activity. Set the following properties:

    Property Value
    CanCreateInstance True (check the checkbox)
    OperationName StartSample
    ServiceContractName ITransactionSample

    The workflow should look like this:

    Adding a Receive activity

  7. Click the Define... link in the Receive activity and make the following settings:

    Setting message settings for the Receive activity

  8. Drag and drop a Sequence activity into the Body section of the TransactedReceiveScope. Within the Sequence activity drag and drop two WriteLine activities and set the Text properties as shown in the following table.

    Activity Value
    1st WriteLine "Service: Receive Completed"
    2nd WriteLine "Service: Received = " + requestMessage

    The workflow should now look like this:

    Sequence after adding WriteLine activities

  9. Drag and drop the PrintTransactionInfo activity after the second WriteLine activity in the Body in the TransactedReceiveScope activity.

    Sequence after adding PrintTransactionInfo

  10. Drag and drop an Assign activity after the PrintTransactionInfo activity and set its properties according to the following table.

    Property Value
    To replyMessage
    Value "Service: Sending reply."

  11. Drag and drop a WriteLine activity after the Assign activity and set its Text property to "Service: Begin reply."

    The workflow should now look like this:

    After adding Assign and WriteLine

  12. Right click the Receive activity and select Create SendReply and paste it after the last WriteLine activity. Click the Define... link in the SendReplyToReceive activity and make the following settings.

    Reply message settings

  13. Drag and drop a WriteLine activity after the SendReplyToReceive activity and set it’s Text property to "Service: Reply sent."

  14. Drag and drop a WriteLine activity at the bottom of the workflow and set its Text property to "Service: Workflow ends, press ENTER to exit."

    The completed service workflow should look like this:

    Complete Service Workflow

Implement the workflow client

  1. Add a new WCF Workflow application, called WorkflowClient to the Common project. To do this right click the Common project, select Add, New Item ..., Select Workflow under Installed Templates and select Activity.

    Add an Activity project

  2. Drag and drop a Sequence activity onto the design surface.

  3. Within the Sequence activity drag and drop a WriteLine activity and set its Text property to "Client: Workflow starting". The workflow should now look like this:

    Add a WriteLine activity

  4. Drag and drop a TransactionScope activity after the WriteLine activity. Select the TransactionScope activity, click the Variables button and add the following variables.

    Add variables to the TransactionScope

  5. Drag and drop a Sequence activity into the body of the TransactionScope activity.

  6. Drag and drop a PrintTransactionInfo activity within the Sequence

  7. Drag and drop a WriteLine activity after the PrintTransactionInfo activity and set its Text property to "Client: Beginning Send". The workflow should now look like this:

    Adding Client: Beginning Send activities

  8. Drag and drop a Send activity after the Assign activity and set the following properties:

    Property Value
    EndpointConfigurationName workflowServiceEndpoint
    OperationName StartSample
    ServiceContractName ITransactionSample

    The workflow should now look like this:

    Setting the Send activity properties

  9. Click the Define... link and make the following settings:

    Send activity message settings

  10. Right click the Send activity and select Create ReceiveReply. The ReceiveReply activity will be automatically placed after the Send activity.

  11. Click the Define... link on the ReceiveReplyForSend activity and make the following settings:

    Setting the ReceiveForSend message settings

  12. Drag and drop a WriteLine activity between the Send and ReceiveReply activities and set its Text property to "Client: Send complete."

  13. Drag and drop a WriteLine activity after the ReceiveReply activity and set its Text property to "Client side: Reply received = " + replyMessage

  14. Drag and drop a PrintTransactionInfo activity after the WriteLine activity.

  15. Drag and drop a WriteLine activity at the end of the workflow and set its Text property to "Client workflow ends." The completed client workflow should look like the following diagram.

    The completed client workflow

  16. Build the solution.

Create the Service application

  1. Add a new Console Application project called Service to the solution. Add references to the following assemblies:

    1. System.Activities.dll

    2. System.ServiceModel.dll

    3. System.ServiceModel.Activities.dll

  2. Open the generated Program.cs file and the following code:

          static void Main()  
      {  
          Console.WriteLine("Building the server.");  
          using (WorkflowServiceHost host = new WorkflowServiceHost(new DeclarativeServiceWorkflow(), new Uri("net.tcp://localhost:8000/TransactedReceiveService/Declarative")))  
          {
              //Start the server  
              host.Open();  
              Console.WriteLine("Service started.");  

              Console.WriteLine();  
              Console.ReadLine();  
              //Shutdown  
              host.Close();  
          };
      }

  3. Add the following app.config file to the project.

    <?xml version="1.0" encoding="utf-8" ?>  
<!-- Copyright © Microsoft Corporation.  All rights reserved. -->  
<configuration>  
    <system.serviceModel>  
        <bindings>  
            <netTcpBinding>  
                <binding transactionFlow="true" />  
            </netTcpBinding>  
        </bindings>  
    </system.serviceModel>  
</configuration>

Create the client application

  1. Add a new Console Application project called Client to the solution. Add a reference to System.Activities.dll.

  2. Open the program.cs file and add the following code.

    class Program  
{  

    private static AutoResetEvent syncEvent = new AutoResetEvent(false);  

    static void Main(string[] args)  
    {  
        //Build client  
        Console.WriteLine("Building the client.");  
        WorkflowApplication client = new WorkflowApplication(new DeclarativeClientWorkflow());  
        client.Completed = Program.Completed;  
        client.Aborted = Program.Aborted;  
        client.OnUnhandledException = Program.OnUnhandledException;  
        //Wait for service to start  
        Console.WriteLine("Press ENTER once service is started.");  
        Console.ReadLine();  

        //Start the client
        Console.WriteLine("Starting the client.");  
        client.Run();  
        syncEvent.WaitOne();  

        //Sample complete  
        Console.WriteLine();  
        Console.WriteLine("Client complete. Press ENTER to exit.");  
        Console.ReadLine();  
    }  

    private static void Completed(WorkflowApplicationCompletedEventArgs e)  
    {  
        Program.syncEvent.Set();  
    }  

    private static void Aborted(WorkflowApplicationAbortedEventArgs e)  
    {  
        Console.WriteLine("Client Aborted: {0}", e.Reason);  
        Program.syncEvent.Set();  
    }  

    private static UnhandledExceptionAction OnUnhandledException(WorkflowApplicationUnhandledExceptionEventArgs e)  
    {  
        Console.WriteLine("Client had an unhandled exception: {0}", e.UnhandledException);  
        return UnhandledExceptionAction.Cancel;  
    }  
}

See also