使用MongoDB和PHP将记录插入嵌套数组

I have a collection in MongoDB called topic

topic{
    topic_title: 'thread',
    reply{
        reply_title: 'thread',
        reply_content: 'content'
        reply_created: "2013-06-18 17:54:04" 
    }

}

I wanted to add a reply to the topic like:

topic{
    topic_title: 'thread',
    reply{
        reply_title: 'thread',
        reply_content: 'content'
        reply_created: "2013-06-18 17:54:04" 
    }
    {
        reply_title: 'reply1',
        reply_content: 'reply2'
        reply_created: "2013-06-18 17:57:04" 
            }
}

my code goes like this:

   $reply = array(
                            "reply_title" => $title,
                            "reply_content" =>$content,
                            "reply_created" => date('Y-m-d H:i:s')
        );
    $document = array('$push' => array("reply" => $reply));

    $id = new MongoId($topicid);
    $topic->update(array("_id"=>$id),$document);

and it did something like this

     topic{
           topic_title: 'replytitle'
           reply {
                    reply_title: "replytitle"
                    reply_content: "replycontent"
                    reply_created: "2013-06-18 17:57:12"
                 }

          }
      reply{
            reply{
                    reply_title: "replytitle"
                    reply_content: "replycontent"
                    reply_created: "2013-06-18 17:57:12"
             }
            reply{
                    reply_title: "replytitle"
                    reply_content: "replycontent"
                    reply_created: "2013-06-18 17:57:12"
             }
           }

I am really having a hard time doing a simple thing. which is add a reply to the reply array. Any help out there?

I'm a little unclear on what your document structure is since what you posted isn't valid JSON. But assuming that topic.reply is supposed to be an array of documents, you can use the $push operator like this:

$topic->update( array( "_id" => $id ), array( "$push" => array( "topic.reply", $reply ) ) );