I run a little script on my server where people can moderate a link (basically up & downvotes). This is run in a CGI::Application I wrote myself, but I'm having a bit of troubles finding a better way to prevent the users from voting multiple times (I don't need top security or anything, I just don't want easy ballotstuffing).

So far, my code looks like this:

sub link_moderate
{
    my $self = shift;
    
    my $q = $self->query();
    my $output = "";
    my $tmpl = $self->load_tmpl('.tmpl');
    
    my $uri = $q->param('uri')||"";
    my $direction = $q->param('direction')||"";
    
    #FIX!! (check for existence of URL)
    
    my $statementHandle = $Database->prepare("SELECT COUNT(*) FROM mod
+eration WHERE userkey LIKE '".$q->remote_addr."-$uri';");
    my $returnValue = $statementHandle->execute;
    
    my @results = $statementHandle->fetchrow_array;
    
    if ($results[0] >= 1)
    {
        $tmpl->param('message' => "Ahem, you've alredy voted at this. 
+Stop doing it, you won't get any further.");
    }
    else
    {
        if ($direction eq "up")
        {
            my $returnValueStatus = $Database->do("UPDATE saved_search
+ SET moderation=moderation+1 WHERE uri LIKE '$uri';");
            $returnValueStatus = $Database->do("INSERT INTO moderation
+ VALUES('".$q->remote_addr."-$uri');");
            
            if ($returnValueStatus == 1)
            {
                $tmpl->param('message' => "The moderation value for th
+e url has been updated.");
            }
            else
            {
                $tmpl->param('message' => "The URL could not be found 
+in the database.");
            }
        }
        elsif ($direction eq "down")
        {
            my $returnValueStatus = $Database->do("UPDATE saved_search
+ SET moderation=moderation-1 WHERE uri LIKE '$uri';");
            $returnValueStatus = $Database->do("INSERT INTO moderation
+ VALUES('".$q->remote_addr."-$uri');");
        
            if ($returnValueStatus == 1)
            {
                $tmpl->param('message' => "The moderation value for th
+e url has been updated.");
            }
            else
            {
                $tmpl->param('message' => "The URL could not be found 
+in the database.");
            }
            
            $Database->do("DELETE FROM saved_search WHERE moderation <
+= -15;");
        }
        else
        {
            $tmpl->param('message' => "Eh, what direction would '$dire
+ction' be?");
        }
    }
    
    $tmpl->param('version' => $VERSION);
    $tmpl->param('number_of_links' => &get_number_of_links);
    $tmpl->param('list_urls' => &getlast(10));
    
    $output = clean_html($tmpl->output);
    
    $self->header_props(-Content_length=>length($output));
    return $output;
}

[download]

As you can see, there goes an awful lot of data into the moderation table, and it's generally not very pretty.

Any thoughts on this?

Edit kudra, 2002-10-27 Added a readmore tag

In reply to Preventing multiple votes by same user effeciently by carthag

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