TAILIEUCHUNG - Using Transactions with a DataSet (SQL)

Using Transactions with a DataSet (SQL) In Chapter 3, "Introduction to Structured Query Language," you saw how you can group SQL statements together into transactions. | Using Transactions with a DataSet SQL In Chapter 3 Introduction to Structured Query Language you saw how you can group SQL statements together into transactions. The transaction is then committed or rolled back as one unit. For example in the case of a banking transaction you might want to withdraw money from one account and deposit it into another account. You would then commit both of these changes as one unit or if there s a problem rollback both changes. In Chapter 8 Executing Database Commands you saw how to use a Transaction object to represent a transaction. As you know a DataSet doesn t have a direct connection to the database. Instead you use the Fill and Update methods of a DataAdapter to pull and push rows from and to the database to your DataSet respectively. In fact a DataSet has no knowledge of the database at all. A DataSet simply stores a disconnected copy of the data. Because of this a DataSet doesn t have any built-in functionality to handle transactions. How then do you use transactions with a DataSet The answer is you must use the Transaction property of the Command objects stored in a DataAdapter. Using the DataAdapter Command Object s Transaction Property A DataAdapter stores four Command objects that you access using the SelectCommand InsertCommand UpdateCommand and DeleteCommand properties. When you call the Update method of a DataAdapter it runs the appropriate InsertCommand UpdateCommand or DeleteCommand. You can create a Transaction object and set the Transaction property of the Command objects in your DataAdapter to this Transaction object. When you then modify your DataSet and push the changes to the database using the Update method of your DataAdapter the changes will use the same Transaction. The following example creates a SqlTransaction object named mySqlTransaction and sets the Transaction property of each of the Command objects in mySqlDataAdapter to mySqlT ransaction SqlTransaction mySqlTransaction .

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