Using Transactions in Perl Programs
Problem
You want to perform a transaction in a DBI script.
Solution
Use the standard DBI transaction support mechanism.
Discussion
The DBI mechanism for performing transactions is based on explicit manipulation of auto-commit mode. The procedure is as follows:
Turn on the
RaiseErrorattribute if it’s not enabled and disablePrintErrorif it’s on. You want errors to raise exceptions without printing anything; leavingPrintErrorenabled can interfere with failure detection in some cases.Disable the
AutoCommitattribute so that a commit will be done only when you say so.Execute the statements that make up the transaction within an
evalblock so that errors raise an exception and terminate the block. The last thing in the block should be a call tocommit( ), which commits the transaction if all its statements completed successfully.After the
evalexecutes, check the$@variable. If$@contains the empty string, the transaction succeeded. Otherwise, theevalwill have failed due to the occurrence of some error and$@will contain an error message. Invokerollback( )to cancel the transaction. If you want to display an error message, print$@before callingrollback( ).
The following code shows how to implement this procedure to perform our example transaction. It does so in such a way that the current values of the error-handling and auto-commit attributes are saved before and restored after executing the transaction. That may be overkill for your own ...