mysqli_real_escape_string（）期望参数1为mysqli，

Question

我的原始代码：

defined('_VALID') or die('Restricted Access!');
define('DEFAULT_CATEGORY', 1);

require $config['BASE_DIR'].'/include/config.aemembedder.php';

Auth::checkAdmin();

$source  = [
    'website' => '', 
    'url' => '', 
    'username' => 'anonymous', 
    'uid' => 1, 
    'category' => '0'
];
$categories = get_categories();
if (isset($_POST['add_source'])) {
    require $config['BASE_DIR'].'/classes/filter.class.php';
    require $config['BASE_DIR'].'/classes/validation.class.php';
    $filter     = new VFilter();
    $valid      = new VValidation();
    $url        = $filter->get('url');
    $username   = $filter->get('username');
    $category   = $filter->get('category');
    $source['url']  = $url; 
    $source['username'] = $username;
    if ($url == '') {
        $errors[]       = 'URL field cannot be left blank!';
        $err['url'] = 1;
    } else {
        $parts = explode('/', str_replace(array('http://www.', 'http://', 'https://www.', 'https://'), '', $url));
        if (isset($parts['0'])) {
            $site = $parts['0'];
            if (!isset($sites[$site])) {
                $errors[] = 'Invalid url! Supported sites: '.implode(', ', $sites).'!';
                $err['url'] = 1;
            } else {
                $source['website'] = $sites[$site];
            }
        } else {
            $errors[] = 'Failed to get site identifier from url!';
            $err['url'] = 1;
        }
    }

    if ($username == '') {
        $errors[]   = 'Username field cannot be left blank!';
        $err['username'] = 1;
    } else {
        $rs = $conn->execute("
            SELECT UID 
            FROM signup 
            WHERE username = '".mysqli_real_escape_string($username)."' 
            LIMIT 1
        ");
        if (!$conn->Affected_Rows()) {
            $errors[] = 'Username is not a valid username on this system!';
            $err['username'] = 1;           
        } else {
            $source['uid']  = (int) $rs->fields['UID'];
    }
}

我收到此错误：

  

警告：mysqli_real_escape_string（）恰好需要2个参数，给定1个

我更改了这一行：

$rs = $conn->execute("
    SELECT UID 
    FROM signup 
    WHERE username = '".mysqli_real_escape_string($username)."' 
    LIMIT 1
");

对此：

$rs = $conn->execute("
    SELECT UID 
    FROM signup 
    WHERE username = '".mysqli_real_escape_string($conn, $username)."' 
    LIMIT 1
");

现在我收到此错误：

  

警告：mysqli_real_escape_string（）期望参数1为mysqli

如何解决？