若检查select查询的语句被忽略

我得到了以下代码：

if(isset($_POST['vote'])){
        if (!$wgUser->isLoggedIn()) {
            // User is not online, don't accept the vote, set error message
            $msg = 'Login required to vote.';
        } if ($wgUser->isBlocked()) {
            // User is banned, don't accept the vote, set error message
            $msg = 'Account is banned.';
        } else {
            // User is online and not banned
            $buildId = htmlspecialchars($_POST['id'], ENT_QUOTES, 'UTF-8');
            $rating = htmlspecialchars($_POST['rating'], ENT_QUOTES, 'UTF-8');
            $comment = htmlspecialchars($_POST['comment'], ENT_QUOTES, 'UTF-8');
            $res = $db->select(
                'build_rating',
                array('article_id', 'username', 'vote', 'comment', 'date'),
                array('article_id' => $buildId, 'username' => $wgUser->getName()),
                __METHOD__
            );
            // Did user already vote on this build?
            if (!$res) {
                // Yes, let's update the vote and set success message
                $db->update(
                    'build_rating',
                    array('vote' => $rating, 'comment' => $comment),
                    array('article_id' => $buildId, 'username' => $wgUser->getName()),
                    __METHOD__
                );
                $msg = 'Your vote has been successfully updated.';
            } else {
                // No, let's insert the vote and set success message
                $db->insert(
                    'build_rating',
                    array('article_id' => $buildId, 'username' => $wgUser->getName(), 'vote' => $rating, 'comment' => $comment),
                    __METHOD__
                );
                $msg = 'Your vote has been successfully saved.';
            }
        }
    }

用于保存用户对特定文章的评分。除了if语句之外，一切似乎都正常工作，if语句检查用户是否已经投票（在这种情况下，它应该更新评级）或是否是全新的投票（在那种情况下，应该将其保存为新的投票）。由于某种原因，if语句不起作用，因为每张选票都被保存为新的选票。一个用户可以简单地放置100个投票，而事实上他应该只能放置一个文章。有人能指出我的错误吗？