如何制作一个PHP数组的多部分帖子数据？

$postData = array();

$postData['title'] = '帖子标题';
$postData['author'] = '作者';
$postData['date'] = '发布日期';

$postData['content'] = '帖子内容';

if(isset($_FILES['attachment'])){
    $file = $_FILES['attachment'];
    $filename = $file['name'];
    $tmpPath = $file['tmp_name'];
    $uploadPath = '路径/到/上传目录/' . $filename;
    move_uploaded_file($tmpPath, $uploadPath);
    $postData['attachment'] = $uploadPath;
}

// 存储到数据库
// $db->insert('posts', $postData);

// 其他处理
// ...