public String getVoteCount() throws ElectionException {
String tmp = "Vote count so far:";
Query q = em.createNamedQuery("Candidate.findAll");
List<Candidate> candidates = q.getResultList();
for (Candidate c : candidates) {
tmp += "\n" + c.getName() + " " + c.getVotes();
}
return tmp;
}
// A transaction is required to update both VOTER and CANDIDATE tables
// Advanced thought: transactional processing should ensure vote count not corrupted
// by multithreading but that may depend on locking strategy of database
// Synchronizing this method could hurt performance at peak voting times
public void castBallot(String voterName, String candidateName)
throws ElectionException, CandidateException {
Query q = em.createNamedQuery("getCandidateByName");
q.setParameter("candidateName", candidateName);
List<Candidate> candidates = q.getResultList();
if (candidates.size() != 1) {
// assuming all candidates have a unique name
throw new ElectionException("Attempt to vote for unknown candidate");
}
Candidate candidate = candidates.get(0);
candidate.setVotes(candidate.getVotes() + 1);
Voter voter = new ElectoralRoll().getVoterByName(em, voterName);
if (voter.isVoted()) {
throw new ElectionException("Attempt to vote twice: " + voterName);
}
voter.setVoted(true);
}