MongoDB / PHP：更新数组的单个值

Greetings,

I have the following mongodb object:

{
   "_id": ObjectId("4d0b9c7a8b012fe287547157"),
   "messages": {
     "0": {
       "toUname": "Eamorr3",
       "fromUname": "Eamorr2",
       "time": 1292606586,
       "id": "j7zwr2hzx14d3sucmvp5",
       "subject": "asdf",
       "message": "asdf",
       "read": 0
    }
  },
   "uname": "Eamorr3"
}

How do I set "read" to 1 in PHP?

Here's what I've tried sofar to no avail:

update(array('uname'=>$uname),array('$set'=>array('messages'=>array('read')=>'1')));

I'm totally stuck. Any help much appreciated.

Many thanks in advance,

I believe it's either

update(array('uname'=>$uname),array('$set'=>array('messages.0'=>array('read')=>'1')));

or

update(array('uname'=>$uname),array('$set'=>array('messages.0.read'=>1));