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DBI.pm  view on Meta::CPAN

  use DBI;
  use vars qw(@ISA);
  @ISA = qw(DBI);

  package MySubDBI::db;
  use vars qw(@ISA);
  @ISA = qw(DBI::db);

  sub prepare {
    my ($dbh, @args) = @_;
    my $sth = $dbh->SUPER::prepare(@args)
        or return;
    $sth->{private_mysubdbi_info} = { foo => 'bar' };
    return $sth;
  }

  package MySubDBI::st;
  use vars qw(@ISA);
  @ISA = qw(DBI::st);

  sub fetch {
    my ($sth, @args) = @_;
    my $row = $sth->SUPER::fetch(@args)
        or return;
    do_something_magical_with_row_data($row)
        or return $sth->set_err(1234, "The magic failed", undef, "fetch");
    return $row;
  }

When calling a SUPER::method that returns a handle, be careful to
check the return value before trying to do other things with it in
your overridden method. This is especially important if you want
to set a hash attribute on the handle, as Perl's autovivification
will bite you by (in)conveniently creating an unblessed hashref,
which your method will then return with usually baffling results
later on.  It's best to check right after the call and return undef
immediately on error, just like DBI would and just like the example
above.

If your method needs to record an error it should call the set_err()