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2. Similar to what you did with the preceding transaction, drag an instance of CompensatableTransactionScope from the Visual Studio Toolbox and drop it between the makeWithdrawal1 activity and the ifElseBranchActivity13 title above makeWithdrawal1.
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3. Drag the makeWithdrawal1 Code activity from below the compensatableTransactionScope1 activity, and drop it into the transaction scope. The MakeWithdrawal method, which is bound to the makeWithdrawal1 activity, now executes its ADO.NET code within an ambient transaction just as the deposit activity did.
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4. However, unlike the deposit functionality, you must provide the compensation logic. The transaction isn t rolled back in the traditional sense. Instead, you need to access the compensatableTransactionScope1 compensation handler and add the compensating function yourself. To do that, move the mouse over the Smart Tag beneath the compensatableTransactionScope1 title in the visual workflow designer and click it once to drop the view menu associated with this activity.
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5. Click the right icon, View Compensation Handler, to activate the compensation handler view.
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6. Drag an instance of the Code activity from the Visual Studio Toolbox, and drop it into the compensation handler activity.
7. For the Code activity s ExecuteCode property, enter CompensateWithdrawal. Visual Studio inserts the method into your source code and switches you to the code editor.
Part III
Workflow Processing
8. Add the following code to the CompensateWithdrawal method you just inserted:
// Here, you "undo" whatever was done that did succeed. The // code that withdrew the money from the account was actually // successful (there is no catch block), so this compensation // is forced. Therefore, we're safe in depositing the amount // that was withdrawn. Note we can't use MakeDeposit since // we require a SQL Server transaction and this method is // called within the compensation handler (i.e., we can't drop // a TransactionScope activity into the compensation to kick // off the SQL Server transaction). We'll create the transaction // ourselves here. // // Craft your compensation handlers carefully. Be sure you know // what was successfully accomplished so that you can undo it // correctly. string connString = ConfigurationManager.ConnectionStrings["BankingDatabase"]. ConnectionString; if (!String.IsNullOrEmpty(connString)) { SqlConnection conn = null; SqlTransaction trans = null; try { // Create the connection conn = new SqlConnection(connString); // Create the command object SqlCommand cmd = new SqlCommand("dbo.Deposit", conn); cmd.CommandType = CommandType.StoredProcedure; // Create and add parameters SqlParameter parm = new SqlParameter("@AccountNo", SqlDbType.Int); parm.Direction = ParameterDirection.Input; parm.Value = _account; cmd.Parameters.Add(parm); parm = new SqlParameter("@ThrowError", SqlDbType.SmallInt); parm.Direction = ParameterDirection.Input; parm.Value = 0; cmd.Parameters.Add(parm); parm = new SqlParameter("@Amount", SqlDbType.Money); parm.Direction = ParameterDirection.Input; parm.Value = CurrentMoneyValue; cmd.Parameters.Add(parm); SqlParameter outParm = new SqlParameter("@Balance", SqlDbType.Money); outParm.Direction = ParameterDirection.Output; outParm.Value = 0; // initialize to invalid cmd.Parameters.Add(outParm); // Open the connection conn.Open();
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// Initiate the SQL transaction trans = conn.BeginTransaction(); cmd.Transaction = trans; // Execute the command cmd.ExecuteNonQuery(); // Commit the SQL transaction trans.Commit();
Workflows and Transactions
// Pull the output parameter and examine CurrentBalance = (decimal)outParm.Value; } // try catch { // Rollback... Note we could issue a workflow exception here // or continue trying to compensate (by writing a transactional // service). It would be wise to notify someone... if (trans != null) trans.Rollback(); } // catch finally { // Close the connection if (conn != null) conn.Close(); } // finally } // if
9. With the compensation code added to your workflow, return to the visual workflow designer and drop an instance of the custom Failed activity into the compensation handler, following the Code activity you just entered. Note Visual Studio might reformat and return you to the top-level state activity layout as you return to the visual workflow designer. If this happens, simply double-click the CmdPressed5 activity in WithdrawState once again to access the compensatableTransactionScope1 activity, and once again select the compensation handler view from its Smart Tag.
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