package Class::Parent;

sub new {
    my $class = shift;
    my ($args) = @_;

    my $self;
    unless (ref $class) {
        $self = {};
        bless $self, $class;
    } else {
        $self = $class;
    }

    my @keys = keys %$args;
    @{$self}{@keys} = @{$args}{@keys};

    # At this point, you have $self blessed into the right
    # class and with the right keys. Specifically, whatever
    # is needed for the DBI.

    # Do DBI thing.

    return $self;
}

package Class::Child;

use Class::Parent;
@ISA = qw(Class::Parent);

sub new {
    my $class = shift;
    my ($args) = @_;

    my $self = {};
    bless $self, ref$class || $class;

    $self->SUPER::new($args);

    # Do whatever else Class::Child needs

    return $self;
}