Managing & Using MySQL, 2nd Edition

Error Handling and Attributes

Because of typos in their programs or problems in setting up their databases, most programmers turn up errors when they first run an example. We’ll look at some ways to deal with errors here. Luckily, the DBI module provides useful diagnostic messages by default.

The connect() method offers an optional argument that controls the attributes of the database handle. Attributes include whether the statement prints an error message in case of failure, whether it throws a potentially fatal exception in case of failure, and many other things. We will not delve into the many subtleties here, such as the varied places where attributes can be set or the ones that statement handles inherit from the database handle. Instead, we will show a couple uses of attributes for error handling.

Suppose you want DBI to terminate your program if it cannot make a connection or if any later DBI method fails. You can put this behavior in your connect( ) command by adding a fourth argument that sets the RaiseError attribute, as follows:

my $dbh = DBI->connect("dbi:mysql:$db:$server", $username, $password,
                       { RaiseError => 1 } );

If you want to do something fancier with attributes, such as set them at runtime, here is the syntax for specifying the attribute argument (it is a reference to a hash):

my %attr = ( RaiseError => 1 );
my $dbh = DBI->connect("dbi:mysql:$db:$server", $username, $password,
                       \%attr);

In either case, running a program with an incorrect password produces the ...