PHP投票功能不起作用

Question

目前我正在尝试为我的网站创建投票功能。现在，投票功能正在运行，但一旦我刷新我的页面，它就会回到默认值。我可以知道如何解决这个问题。

这是我的PHP代码：

<?php
$db = getConnection();

$sql = "SELECT * FROM photos ";

$result = $db->prepare($sql);


$result->execute();

while ($row = $result->fetch(PDO::FETCH_ASSOC)) {

      ?>
      <div class="item" data-postid="<?php echo $row['photoID'] ?>" 
        data-score="<?php echo $row['vote'] ?>"> <!-- Thus line shows the row id and the vote score -->
        <div class="vote-span"><!-- voting-->
          <div class="vote" data-action="up" title="Vote up">
            <i class="icon-chevron-up"></i>
          </div><!--vote up-->
          <div class="vote-score"><?php echo $row['vote'] ?></div>
          <div class="vote" data-action="down" title="Vote down">
            <i class="icon-chevron-down"></i>
          </div><!--vote down-->
        </div>
<?php
//echo $row['eventName'];
$photoPath = $row['photoPath'];

    echo "<div class='row'>
               <a href='$photoPath' data-toggle='lightbox'>
                  <img class='img-thumbnail' src='$photoPath' alt='' width='300' height='300'>
               </a>
          </div>
        </div>";

}
?>

这是ajax代码：

if($_SERVER['HTTP_X_REQUESTED_WITH']){
if(isset($_POST['postid']) AND isset($_POST['action'])){
    $postid = $_POST['postid'];
    $db = getConnection();
    $db->quote($postid);
    if(isset($_SESSION['vote'][$postid])) return;

    $sql="SELECT * FROM photos WHERE photoID ='{$postid}'
         LIMIT 1";
    $result = $db->prepare($sql);
    $result->execute();
    if($rows = $result->fetch(PDO::FETCH_ASSOC)){
        if($_POST['action'] === 'up'){
            $vote = ++$rows['vote'];
        }else{
            $vote = --$rows['vote'];
        }

        $sqlupdate = "UPDATE photos SET vote = '{$vote}'
                        WHERE photoID = '{$postid}'";
        $result = $db->prepare($sqlupdate);
        $result->execute();

        $_SESSION['vote'][$postid] = true;


    }
}
}