优化包含 PDO 查询的 while 循环

Question

信息

目前正在构建一个通知页面，其中列出了所有登录的用户通知，其中包含有关每个通知的信息。

例如，没有信息

You have an unread message

有信息

<Sarah> Sent you an message

问题

因为通知需要用户名（用于消息通知）或文章标题（比如您关注作者并且他们发布了新博客文章）等数据，所以一个通知需要从用户表中提取用户名，然后还需要标题来自博客表的博客）这会导致我的页面甚至在本地主机上滞后，我猜一旦上传并在野外测试会变得更糟。

当前代码

function showNotifications($userid){
    $STH = $this->database->prepare('SELECT * FROM notifications WHERE user_id = :userid ORDER BY timestamp DESC');
    $STH->execute(array(':userid' => $userid));
    while($row = $STH->fetch(PDO::FETCH_ASSOC)){
        $this->sortNotif($row);
}

关于下面函数的快速解释，因为我有不同类型的通知我为特定类型创建了一堆 ID，例如 type 1 = new message，type 2 = new blog post

function sortNotif($notif){

    switch ($notif['type']) {

        case "1":
            $msg = $this->getMessageData($notif['feature_id']);
            $user = $this->userData($msg['sender']);
            echo '<li><i>'.timeAgo($notif['timestamp']).'</i><a href="user.php?username='.$user['username'].'">'.$user['first_name'].'</a> sent you a <a href="inbox.php?message='.$msg['id'].'">message</a></li>';
            break;

    }

}

正如您所看到的，仅显示用户有一条新消息它会创建 2 个查询，并且一旦循环通过 40 个左右的通知，超过 100 个左右的用户就会对服务器造成压力。

结束语

如果有人需要更多信息，请询问，我一定会尽快更新此问题，谢谢！

编辑

以下是以下 cmets 中要求的表结构。

通知

id | user_id | feature_id | type | timestamp | read

用户

id | username | password | first_name | last_name | email | verify_hash | avatar | type 

消息

id | receiver | sender | replying_to | deleted | body | timestamp | read

Answer 1

计划改变，因为我误解了设置。

您将希望一次性从每个“类型”表中提取所有数据，而不是基于每个通知。这意味着您需要循环两次通知，一次获取所有 id 和适当的类型，然后第二次输出结果。

function showNotifications($userid){
    $STH = $this->database->prepare('SELECT * FROM notifications WHERE user_id = :userid ORDER BY timestamp DESC');
    $STH->execute(array(':userid' => $userid));

    // Centralized Book keeping for the types.
    // When you add a new type to the entire system, add it here as well.
    $types = array();

    // Add the first notification type
    $types["1"] = array();
    // "query" is pulling all the data you need concerning a notification
    $types["1"]["query"] = "SELECT m.id, u.username, u.firstname FROM messages m, users u WHERE m.sender = u.id AND m.id IN ";
    // "ids" will hold the relevant ids that you need to look up.
    $types["1"]["ids"] = array();

    // A second type, just for show.
    // $types["2"] = array();
    // $types["2"]["query"] = "SELECT a.id, u.username, u.firstname FROM articles a, users u WHERE a.sender = u.id AND a.id IN ";
    // $types["2"]["ids"] = array();

    // Use fetchAll to gather all of the notifications into an array
    $notifications = $STH->fetchAll();

    // Walk through the notifications array, placing the notification id into the corret
    // "ids" array in the $types array.
    for($i=0; $i< count($notifications); $i++){
        $types[$notifications[$i]['type']]["ids"][] = $notifications[$i]['feature_id'];
    }

    // Walk through the types array, hit the database once for each type of notification that has ids.
    foreach($types as $type_id => $type){
        if(count($type["ids"]) >  0){
            $STH = $this->database->prepare($type["query"] . "( " . implode(",", $type["ids"]) . " )");
            $STH->execute();
            // Creates a hash table with the primary key as the array key
            $types[$type_id]['details'] = $STH->fetchAll(PDO::FETCH_GROUP|PDO::FETCH_ASSOC); 
            $types[$type_id]['details'] = array_map('reset', $types[$type_id]['details']);
            // run array_map to make it easier to work with, otherwise it looks like this:
            // $results = array(
            //     1234 => array(0 => array('username' => 'abc', 'firstname' => '[...]')),
            //     1235 => array(0 => array('username' => 'def', 'firstname' => '[...]')),
            // );
        }
    }

    // Now walk through notifications again and write out based on notification type,
    // referencing $types[<notification type>]["details"][<message id>] for the details
    for($i=0; $i< count($notifications); $i++){

        // check to see if details for the specific notification exist.
        if(isset($types[$notifications[$i]['type']]["details"][$notifications[$i]['feature_id']])){
            $notification_details = $types[$notifications[$i]['type']]["details"][$notifications[$i]['feature_id']];

            switch ($notifications[$i]['type']) {

                case "1":
                    echo '<li><i>'.timeAgo($notifications[$i]['timestamp']).'</i><a href="user.php?username=' . $notification_details['username'] . '">' . $notification_details['first_name'].'</a> sent you a <a href="inbox.php?message='.$notifications[$i]['feature_id'].'">message</a></li>';
                break;

            }
        }
    }
}

更新：添加了逻辑以在未提取任何详细信息时跳过通知（例如，消息或用户已被删除）

我认为您想运行一个查询，通过连接或更复杂的 where 语句收集所有信息。

选项 1：这可能需要调整，以便不是表格的笛卡尔积

SELECT n.id, n.type, m.id, m.body, u.username, u.first_name 
FROM notifications n, messages m, users u
WHERE n.user_id = :userid AND m.id = n.feature_id AND u.id = m.sender

选项 2：如果表别名不起作用，那么您需要用完整的表名替换它们

SELECT SELECT n.id, n.type, m.id, m.body, u.username, u.first_name 
FROM notifications n
    JOIN messages m
        ON n.feature_id = m.id
    JOIN users u
        ON m.sender = u.id
WHERE n.user_id = :userid