我正在尝试执行一些查询以获取有关某些图像的信息页面。我写了一个函数

function get_recent_highs($view_deleted_images=false)
{
    $lower = $this->database->conn->real_escape_string($this->page_size * ($this->page_number - 1));
    $query = "SELECT image_id, date_uploaded FROM `images` ORDER BY ((SELECT SUM( image_id=`images`.image_id ) FROM `image_votes` AS score) / (SELECT DATEDIFF( NOW( ) , date_uploaded ) AS diff)) DESC LIMIT " . $this->page_size . " OFFSET $lower"; //move to database class
    $result = $this->database->query($query);
    $page = array();
    while($row = $result->fetch_assoc())
    {
        try
        {
            array_push($page, new Image($row['image_id'], $view_deleted_images));
        }
        catch(ImageNotFoundException $e)
        {
            throw $e;
        }
    }
    return $page;
}

根据这些图片的受欢迎程度选择页面。我已经编写了一个Database处理与数据库交互的Image类，并保存了有关图像的信息。当我尝试运行此程序时，出现错误。

Fatal error: Call to a member function fetch_assoc() on a non-object

$result 是mysqli结果集，所以我对为什么它不起作用感到困惑。