Build a Perl/CGI Voting System

The MLDBM module allows complex Perl hashes to be almost seamlessly stored in a local file. The MLDBM::Sync module makes it possible to safely lock these file, using the $sync->Lock and $sync->ReadLock methods. After loading or saving the structure of interest, a subsequent call to the UnLock() method flushes I/O and unties the variable. (See the Perl documentation regarding the MLDBM::Sync module for more information -- man 3 MLDBM::Sync.)

Essentially, the logic flow is as simple as that shown in Listing 1.

1  unless( defined( $q->param( $vparm ) )){

2      # Display initial voting stuff here

3      # select a candidate

4      $ballotBox->printForm( $q );

5  } else {

6      # if vote is tallied, do _not_ mail a ballot

7      if( $castBallot->voteIsTallied( $q ) ){

8           print "Your vote has already been recorded"

9      } else {

10          #

11          # vote not tallied yet, check if we have a draft ballot on file

12          # and move the draftBallot into the castBallot object

13          #

14          if( $draftBallot->exactMatch( $q ) ){

15              # cast ballot

16              print $q->h2('Thank you, your vote has been recorded.');

17              # add the vote to the cast ballot db file

18              $castBallot->tallyVote( $q );

19              # sum up all votes

20              $ballotBox->addVotes( $castBallot );

21              $cc_msg->send();

22          } elsif ( $draftBallot->voter_is_okay( $voter_email )){

23              # Send e-mail to allow voter to confirm vote

24              $mime_msg->send()

25          } else {

26              print 'Only University ballots are acceptable';

27          }

28      }

29  }

Once I had decided what the underlying conditional flow would be, the only remaining task was to construct objects that would fit into this sequence of actions. As I noted previously, the necessary hash data structures were retrieved and updated using tie'd variables and MLDBM file locking. The objects used were more like smart structures than full-fledged objects; the data was passed between them in a way that paralleled the progress of a ballot from an initial draft to a final counted vote.

In other words, the list of ballots was used to construct a DraftBallot, which in turn was used to create the CastBallot and BallotBox classes. In this way there was minimal coupling to the main ballot CGI program.

On another tangent, while I understand that it is generally considered poor practice to have constructors that rely on external resources such as files (since they could fail and wind up in an unpredictable state), the code in this case was much easier to understand by doing just that. Since Perl doesn't rely on pointers, I can see no reason not to take advantage of this simplification.

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