什么是非对象的属性？

Question

我无法理解这个错误。

  

PHP错误：尝试获取非对象的属性

此行显示错误：if ($data->num_rows > 0)

我是php的新手，所以我很难解决这个问题。

源代码：

<?php
if (isset($_GET["token"]) && isset($_GET["email"])) {
    $connection = new mysqli("localhost", "root", "", "hackathon");

    $email = $connection->real_escape_string($_GET["email"]);
    $token = $connection->real_escape_string($_GET["token"]);

    $data = $connection->query("SELECT id 
                                FROM registration 
                                WHERE email='$email' 
                                AND token='$token' 
                                AND token <> '' 
                                AND expire> NOW()");

    if ($data->num_rows > 0) { //   Error in this line
        $str = "0123456789qwertzuioplkjhgfdsayxcvbnm";
        $str = str_shuffle($str);
        $str = substr($str, 0, 15);

        $password = sha1($str);

        $connection->query("UPDATE registration SET password = '$password', token = '' WHERE email='$email'");

        echo "Your new password is: $str";
    } else {
        echo "Please check your link!";
    }
} else {
    header("Location: index.php");
    exit();
}
 ?>