app\models\Contest::vote PHP Method

    public function vote(User $user, ContestEntry $entry)
    {
        $vote = $this->votes()->where('user_id', $user->user_id)->where('contest_entry_id', $entry->id);
        if ($vote->exists()) {
            $vote->delete();
        } else {
            // there's probably a race-condition here, but abusing this just results in the user diluting their vote... so *shrug*
            if ($this->votes()->where('user_id', $user->user_id)->count() < $this->max_votes) {
                $this->votes()->create(['user_id' => $user->user_id, 'contest_entry_id' => $entry->id]);
            }
        }
    }