php – 在设定的到期时间后删除数据库行(例如5分钟)

背景：我正在设计一个在线虚拟教室管理系统……当教师创建教室并将其存储在数据库中时,它可以生成随机会话密钥(md5(时间)).

为了访问教室,学生访问唯一的教室URL,代码将URL中的会话密钥(使用GET)与数据库中的会话密钥进行比较.如果匹配则教室显示.

网址通常如下所示：/classroom.php？Instance = a529501db8373609f2d47a7843a461ea

需要编码帮助：我希望我的老师也能够设置会话“长度”,因此教室可以访问15分钟,25分钟或50分钟.

当创建教室以来的时间超过例如25分钟时,会话密钥将从数据库中删除,并且无法再访问教室.

到目前为止我所拥有的：

当教师单击按钮创建一个classroo时,下面的PHP将会话密钥($instance)和会话长度($duration)存储在数据库中……

<?php
session_start();
if (isset($_SESSION['id'])) {
    if (isset($_POST['hidden'])) {

        // Connects to the database
        include_once("$_SERVER[DOCUMENT_ROOT]/classes/includes/dbconnect.php");
        mysql_connect(DB_HOST,DB_USER,DB_PASSWORD,DB_NAME);

        // Sets the session duration
        $currentTime = time();
        $duration = $currentTime + $_POST['duration'];

        // Session variables
        $uid = $_SESSION['id'];
        $usname = $_SESSION['username'];

        // To generate the random hash from the current time
        $time = time(); // time to hash
        $instance = md5($time); // hash stored in variable

        // Stores the session hash (instance) and duration in the instance database
        $query = ("INSERT INTO `my-db-name-foo`.`instances` (`instance`,`expiry`) VALUES (`$instance`,$duration`);");
        mysql_query($query) or die(mysql_error());

        // Closes the database connection
        mysql_close();

        // Redirects the teacher header('Location:classroom.php?instance='.$instance);
    } 
} else {
    echo 'Please login';
    die();
}
?>

然后在实际的classroom.php页面上,一段代码检查会话是否已过期……如果是,则将其从数据库中删除.

<?php 

$currentTime = time();

if ($currentTime > $duration){
    // Connect to database and delete the row
} else {
    // show the classroom
}
?>

任何帮助或建议将不胜感激！

更新—-

感谢所有伟大的答案,这就是目前这一切的工作原理……

在createclassroom.php页面上,我存储实例以及NOW()日期和时间以及持续时间为NOW()$_POST [‘duration’]; …

<?php
session_start();
if (isset($_SESSION['id'])) {
    if (isset($_POST['duration']) && !EMPTY($_POST['duration'])) {

        // Connects to the database
        include_once("$_SERVER[DOCUMENT_ROOT]/classes/includes/dbconnect.php");

        // Session variables
        $uid = $_SESSION['id'];
        $usname = $_SESSION['username'];

        // To generate the random hash from the current time
        $time = time(); // time to hash
        $instance = md5($time); // hash stored in variable

        // $duration = $_POST['duration'];
        $duration = $_POST['duration'];

        // Stores the hash (instance) in the instance database
        $sql = ("INSERT INTO `xxx_xxxx`.`instances` (`id`,`teacher`,`instance`,`startdate`,`expiredate`) VALUES ('$uid','$usname','$instance',NOW(),NOW() + $duration);");
        $query = mysqli_query($dbConnect,$sql)or die(mysql_error());

        // Redirects the teacher        
        header('Location:classroom.php?instance='.$instance);
    }  else if (isset($_POST['hidden'])) {
        echo 'Please select a duration';
    }
} else {
    echo 'Please login';
    die();
}
?>

在实际的classroom.php页面上,我只检查未过期的会话实例.

<?php 
session_start();

// Connects to the database
include_once("$_SERVER[DOCUMENT_ROOT]/classes/includes/dbconnect.php");

$instance = $_GET['instance']; // GETs instance from URL
$usname = $_SESSION['username']; // Gets teacher name

// script to retrieve all the Instances in the database and store them in a variable '$dbInstance'
$sql = "SELECT instance,expiredate FROM instances WHERE instance = '$instance' AND instances.expiredate > NOW()";
$query = mysqli_query($dbConnect,$sql);
$row = mysqli_fetch_row($query);

$dbInstance = $row[0];

if ($dbInstance == $instance){
    echo $dbInstance.'<br>';
    echo $instance;
} else {
    echo $dbInstance.'<br>';
    echo $instance.'<br>';
    die('Instance not initiated');
}
?>

现在我只需要决定如何经常清理数据库.真的,我想感谢你们的帮助,正是我需要的！