create 2d barcode c# Part III in Visual C#.NET

Creating UCC - 12 in Visual C#.NET Part III

Part III
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To be sure both updates are successful, a transaction comes into play. A transaction itself is a single unit of work that either completely succeeds or completely fails. That s not to say you can t update two different database tables. It just means that both table updates are considered a single unit of work, and both must be updated or else neither one is. If either or both updates fail, ideally you want the system to return to its state just prior to your attempt to update the tables. Your application should move forward with no evidence that there had been an incomplete attempt to modify the tables, and more important, you don t want to have data from the unsuccessful update in one table but not in the other. Note Entire volumes have been written about transactions and transactional processing. Although I ll describe the concepts in sufficient depth to explain how Microsoft Windows Workflow Foundation (WF) supports transactions, I cannot possibly cover transactional processing in great depth in this book. If you haven t reviewed general transactional support in .NET 2.0, you should do so. WF transactions model .NET 2.0 transactional support very closely, and you might find the information in the following article helpful to understanding WF transactional support: msdn2.microsoft.com/en-us/library/ms973865.aspx. Traditionally, transactions have come in a single form that of the XA, or two-phase commit, style of transaction. However, with the advent of Internet-based communication and the need to commit long-running transactions, a newer style of transaction was introduced known as the compensated transaction. WF supports both styles. We ll first discuss the classical transaction, and then after noting the conditions that make this type of transaction a poor architectural choice, we ll discuss the compensated transaction.
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The first system known to have implemented transactional processing was an airline reservation system. Reservations that required multiple flights could not progress if any of the individual flights could not be booked. The architects of that system knew this and designed a transactional approach that today we know as the. X/Open Distributed Transaction Processing Model, known as XA. (See en.wikipedia.org/wiki/X/Open_XA.) An XA transaction involves the XA protocol, which is the two-phase commit I mentioned earlier, and three entities: the application, resource, and transactional manager. The application is, well, your application. The resource is a software system that is designed to join in XAstyle transactions, which is to say it enlists (joins) in the transaction and understands how to participate in the two phases of committing data as well as provides for durability (discussed shortly). The transactional manager oversees the entire transactional process. So what is a two-phase commit In the end, imagine your application needs to write data to, say, a database. If that write is performed under the guise of a transaction, the database holds the data to be written until the transactional manager issues a prepare instruction. At that point, the database responds with a vote. If the vote is to go ahead and commit (write) the data into a table, the transaction manager proceeds to the next participating resource, if any.
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15
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If all resources vote to commit the data, the transactional manager issues a commit instruction and each resource writes the data into its internal data store. Only then is the data destined for your table actually inserted into the database. If any one resource has a problem and votes not to commit the data, the transactional manager issues a rollback instruction. All resources participating in the transaction must then destroy the information related to the transaction, and nothing is permanently recorded. Once the data has been committed, the XA protocol guarantees that the result of the transaction is permanent. If data was inserted, it is there for your application to use. If information was deleted, it has been deleted permanently. Your application, then, can move forward comfortable in the knowledge that all is well with the data. The data is consistent, and the application is in a determinate state.
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