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Cancels the transaction by undoing all logged changes
The database whose changes you want to rollback.
A transaction works by logging all changes. If an error occurs while attempting one of the changes, or the changes need to be undone for some other reason, the transaction is canceled by calling the rollback( ) method. Otherwise, commit( ) is called to clear the transaction log, thereby indicating that all the changes in the transaction were committed and that the transaction as a whole was posted.
Since new rows have already been written to disk, rows that were added during the transaction are deleted. In the case of DBF (dBASE) tables, the rows are marked as deleted, but are not physically removed from the table. If you want to actually remove them, you can pack the table with packTable( ). Rows that were just edited are returned to their saved values.
All locks made during a transaction are maintained until the transaction is completed. This ensures that no one else can make any changes until the transaction is committed or abandoned.