Programming the Perl DBI

Automatic error checking

The automatic error checking capabilities of the DBI operates on two levels. The PrintError handle attribute tells DBI to call the Perl warn( ) function (which typically results in errors being printed to the screen when encountered) and the RaiseError handle attribute (which tells DBI to call the Perl die( ) function upon error, typically causing the script to immediately abort).

Because the standard Perl functions of warn( ) and die( ) are used, you can change the effects of PrintError and RaiseError with the $SIG{_ _WARN_ _} and $SIG{_ _DIE_ _} signal handlers. Similarly, a die( ) from RaiseError can be caught via eval { ... }.

These different levels of automatic error checking can be turned on for any handle, although database handles are usually the most common and useful. To enable the style of automatic error checking you want, you may set the value of either of the following two attributes:

$h->{PrintError} = 1;
$h->{RaiseError} = 1;

Similarly, to disable automatic error checking, simply set the value of these attributes to 0.

If both RaiseError and PrintError are enabled, an error will cause warn( ) and die( ) to be executed sequentially. If no $SIG{_ _DIE_ _} handle has been defined, warn( ) is skipped to avoid the error message being printed twice.^[39]

A more common way in which these attributes are used is to specify them in the optional attribute hash supplied to DBI->connect( ) when connecting to a database. Automatic error checking is the ...