{ # This code implement the transactionalize { ... } using ( dbh );
      my (@dbh_AO,$dbh_HRef,$error_E);
      sub transactionalize(&;$) {
          my ($body_CRef,$dbh_CRef)=@_;
  
          eval {
              ### Setting dbh_O ...
              push(@dbh_AO,(defined $dbh_CRef) ? $dbh_CRef->() : $Defaultdbh_O);
              local $dbh_AO[-1]->{RaiseError}=1;
              warn "@dbh_AO ";
              ### BEGIN TRANSACTION ...
              unless (exists $dbh_HRef->{$dbh_AO[-1]}) {
                  $dbh_AO[-1]->begin_work;
                  $dbh_HRef->{$dbh_AO[-1]}=$dbh_AO[-1];
                   };
  
              ### Do the stuff here ...
              $body_CRef->();
  
              ### COMMIT TRANSACTION ...
              if (@dbh_AO == 1) {
                  for my $dbh_s (keys %$dbh_HRef) {
                      ### $dbh_s
                      $dbh_HRef->{$dbh_s}->commit();
                       };
                   };
              pop(@dbh_AO);
               };
          if ($@) {
              $error_E||=$@;
              ### ROLLBACK TRANSACTION ...
              if (@dbh_AO == 1) {
                  for my $dbh_s (keys %$dbh_HRef) {
                      ### $dbh_s
                      eval { $dbh_HRef->{$dbh_s}->rollback(); };
                       };
                   };
              pop(@dbh_AO);
              Carp::confess $error_E;
               };
           } # transactionalize {}:
  
      sub using($) {
          my $dbh_O=shift;
          ### <where>: $dbh_O
          return sub { return $dbh_O; };
           };
  
       };