Perl Singleton Objects

This is a quick introduction to perl Singleton objects. A singleton object is an object that is only instantiated once throughout an application.

Singleton Uses

Singletons can be used for many things. If you only want one database connection for a particular application, or a limited number of connections a singleton database class can handle managing your open connections.

How to implement

The following is an example of how to put together a database object that opens a database connection and returns an existing connection to the caller.This allows your userid/password to be set in a single location as well. You don't have to have every piece of code that accesses the database use userid/password. Just use the DBConnector object and then issue your database calls.

    package DBconnector;

    my $singleton;

    sub new {
        my $class = shift;
        $singleton ||= bless {}, $class;
    }

    sub connect {
        my $self = shift;
                if (exists $self->{dbh}) {
                  $self->{dbh};
                } else {
                   my $connection = "dbi:mysql:host=$self->{host} \
                   dbname=$self->{name}";
                   $self->{dbh} =  DBI->connect($connection, \
                   $self->{user},$self->{password});
            }
    }
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Summary

There are many ways to use singletons. This is just a basic example, but provides what is needed to create a singleton object.