PHP中的MongoDB - 如何将项目插入集合中的数组?

This has to be easy, but i can't seem to figure it out... Let say i had a collection users and this is the first item in the collection:

{ 
    "_id" : ObjectId("4d8653c027d02a6437bc89ca"), 
    "name" : "Oscar Godson", 
    "email" : "oscargodson@xxx.com", 
    "password" : "xxxxxx", 
    "tasks" : [
    {
        "task" : "pick up stuff",
        "comment" : "the one stuff over there"
    },
    {
        "task" : "do more stuff",
        "comment" : "lots and lots of stuff"
    }
] }

然后我将如何使用 MongoDB 的 PHP 驱动程序将另一个任务"添加到集合中此项的任务"数组中

$new_task = array(
  "task" => "do even more stuff",
  "comment" => "this is the new task added"
);
$collection->update(
  array("_id" => ObjectId("4d8653c027d02a6437bc89ca")), 
  array('$push' => array("tasks" => $new_task))
);