c# pdf417 open source Figure 4-11. Using ServicedDataPortal to wrap a business object in a transaction in C#.NET

Create PDF-417 2d barcode in C#.NET Figure 4-11. Using ServicedDataPortal to wrap a business object in a transaction

Figure 4-11. Using ServicedDataPortal to wrap a business object in a transaction
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Once the transactional context is established by ServicedDataPortal, all normal .NET objects invoked from that point forward run within the same context. ServicedDataPortal itself inherits from System.EnterpriseServices.ServicedComponent, and includes some key attributes:
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[Transaction(TransactionOption.Required)] [EventTrackingEnabled(true)] [ComVisible(true)] public class ServicedDataPortal : ServicedComponent, IDataPortalServer { } The [Transaction()] attribute specifies that this object must run within a COM+ transactional context. If it is called by another object that already established such a context, this object will run within that context; otherwise, it will create a new context. The [EventTrackingEnabled()] attribute indicates that this object will interact with COM+ to enable the spinning balls in the Component Services management console. This is only important (or even visible) if the data portal is running within COM+ on the server meaning that the EnterpriseServicesProxy is used by the client to interact with the server. The [ComVisible()] attribute makes this class visible to COM, which is a requirement for any class that is to be hosted in COM+. Because ServicedDataPortal inherits from ServicedComponent, the Csla.dll assembly itself must be configured so it can be hosted in COM+. Because the assembly already includes the Csla. Server.Hosts.EnterpriseServicesPortal class, all the necessary configuration already exists. This was discussed earlier in the chapter. The class also implements the IDataPortalServer interface, ensuring that it implements the four data methods. Each of these methods has another Enterprise Services attribute: [AutoComplete()]: [AutoComplete(true)] public DataPortalResult Create( Type objectType, object criteria, DataPortalContext context) { SimpleDataPortal portal = new SimpleDataPortal(); return portal.Create(objectType, criteria, context); } The [AutoComplete()] attribute is used to tell COM+ that this method will vote to commit the transaction unless it throws an exception. In other words, if an exception is thrown, the method votes to roll back the transaction; otherwise, it votes to commit the transaction. This fits with the overall model of the data portal, which relies on the business object to throw exceptions in case of failure. The data portal uses the exception to return important information about the failure back to the client. ServicedDataPortal also relies on the exception to tell COM+ to roll back the transaction. Notice how the Create() method simply creates an instance of SimpleDataPortal and delegates the call to that object. This is the same as Csla.Server.DataPortal did for manual transactions; except in this case, SimpleDataPortal and the business object are wrapped in a distributed transactional context. The other three data methods are implemented in the same manner.
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Csla.Server.TransactionalDataPortal
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The TransactionalDataPortal is designed in a manner very similar to ServicedDataPortal. Rather than using Enterprise Services, however, this object uses the transactional capabilities provided by the new System.Transactions namespace, and in particular the new TransactionScope object. This class simply implements IDataPortalServer: public class TransactionalDataPortal : IDataPortalServer { }
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This ensures that it implements the four data methods. Each of these methods follows the same structure: create a TransactionScope object and delegate the call to an instance of Simple DataPortal. For instance, here s the Create() method: public DataPortalResult Create( System.Type objectType, object criteria, DataPortalContext context) { DataPortalResult result; using (TransactionScope tr = new TransactionScope()) { SimpleDataPortal portal = new SimpleDataPortal(); result = portal.Create(objectType, criteria, context); tr.Complete(); } return result; } The first thing this method does is create a TransactionScope object from the System. Transactions namespace. Just the act of instantiating such an object creates a transactional context. It is not a distributed transactional context, but is a lighter-weight context. If the business object interacts with more than one database, however, it will automatically become a distributed transaction. The using block here ensures both that the TransactionScope object will be properly disposed, and perhaps more importantly, that the transaction will be committed or rolled back as appropriate. If the object is disposed before the Complete() method is called, then the transaction is rolled back. Again, this model relies on the underlying assumption that the business code will throw an exception to indicate failure. This is the same model that is used by ServicedDataPortal, and really by the data portal infrastructure overall. Within the using block, the code creates an instance of SimpleDataPortal and delegates the call to that object, which in turn calls the business object. Assuming no exception is thrown by the business object, the Complete() method is called to indicate that the transaction should be committed. The other three methods are implemented in the same manner. Regardless of which transactional model is used, all calls end up being handled by a SimpleDataPortal object, which implements the message router concept.
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