Restore tables to their condition at the beginning of a transaction
ROLLBACK [<workarea | alias> | (<expC>)]
The ROLLBACK command is used in a BEGIN TRANSACTION ... END TRANSACTION block to roll back changes made to tables by any transaction performed between the two statements. ROLLBACK used by itself affects all open tables, but can be directed to a single table by specifying the <.dbf filename>. The filename can be substituted with an <expC>, enclosed in round brackets, which returns a valid filename. A 'transaction' is considered to be all the file modifications that occur within the commands BEGIN TRANSACTION and END TRANSACTION.
This command is particularly useful if an error occurs during a program modifying files. When BEGIN TRANSACTION is issued, all currently open files and all files opened between BEGIN and END TRANSACTION will have Before Image Journaling (BIJ) invoked automatically. The journals are stored in a log file <.log> that the Lianja/4GL generates automatically. You can optionally specify the disk and directory path if you include them after the BEGIN TRANSACTION statement. If BIJ is not required on a particular file, then the command RESET IN <workarea> should be issued and journaling will no longer occur in that workarea.
The ROLLBACK() function returns .T. if a rollback succeeds. The COMPLETED() function can be used after the END TRANSACTION command to determine if any errors occurred during processing of the commands between BEGIN and END TRANSACTION. It returns .F. if errors occurred and .T. otherwise. If the command SET ROLLBACK is OFF, the COMPLETED() function can be used in conjunction with the ROLLBACK command to force a manual rollback. If SET ROLLBACK is ON and an error is encountered, any modifications to files within the transaction will be rolled back automatically to their state before the BEGIN TRANSACTION was executed.
Please note the following commands are not allowed during a transaction:
- CLEAR ALL
- CLOSE ALL
- CLOSE DATABASE
- CLOSE INDEX
- MODIFY STRUCTURE
procedure recovery rollback if rollback() dialog box "Rollback was ok." else dialog box "Rollback not completed." endif return use setcomm on error do recovery begin transaction delete first 15 replace all t1 with (t2*t3)/100 list end transaction if completed() dialog box "Transaction completed" else dialog box "Errors occurred during transaction" endif