PHP将XML文件导入数据库

I am attempting to allow users to upload a file, the contents of which would then be read into a database using SimpleXML. My code is as follows:

else
{
    $info = pathinfo($_FILES['xml_file']['tmp_name']);
    $extension = $info['extension'];

    if($extension != 'xml')
    {
        flash_message($lang->wiki_invalid_file, 'error');
        admin_redirect('index.php?module=wiki-import');
    }
    else
    {
        if($_FILES['xml_file']['error'] == UPLOAD_ERR_OK && is_uploaded_file($_FILES['xml_file']['tmp_name']))
        {
            $string = file_get_contents($_FILES['xml_file']['tmp_name']);
            $xml = new SimpleXMLElement($string);
            foreach($xml->article as $article)
            {
                $query = "INSERT INTO " . TABLE_PREFIX . "wiki('authors','title','content','protected','lastauthor','lastauthorid','category') VALUES('" . $article->authors . "','" . $article->title . "','" . $article->content . "','" . $article->protected . "','" . $article->lastauthor . "','" . $article->lastauthorid . "','" . $article->category . "',)";
                $sql = $db->write_query($query);
                if($db->error_number() > 0)
                {
                    flash_message($lang->wiki_import_error, 'error');
                    admin_redirect('index.php?module=wiki-import');
                }
                elseif(!$sql)
                {
                    flash_message($lang->wiki_import_error, 'error');
                    admin_redirect('index.php?module=wiki-import');
                }
                else
                {
                    flash_message($lang->wiki_import_success, 'success');
                    admin_redirect('index.php?module=wiki-import');
                }
            }
        }
        else
        {
            flash_message($lang->wiki_import_error, 'error');
            admin_redirect('index.php?module=wiki-import');
        }
    }
}

(I am using MyBB, which has definitions for flash_message and admin_redirect, which redirects the user to another page and displays a message.)

My issue is that I cannot seem to upload it at all, no error message is shown. In addition, the page just refreshes. A sample piece of content is:

<?xml version="1.0" ?>
<wiki>
    <article>
        <id>1</id>
        <title>To be Exported</title>
        <content>
            Export me!
        </content>
        <category>Meta</category>
        <lastauthor>admin</lastauthor>
        <lastauthorid>1</lastauthorid>
        <protected>0</protected>
        <authors>1</authors>
    </article>
</wiki>

The id and name attribute of the file upload box is 'xml_file'. I also have PHP version 5.3.13 on my localhost.