PHP/MongoDB - Add subdocument to document with _id -

i trying learn mongodb php. can save new document ->save($object). goal add subdocument document specific _id.

i have document:

"5197f4bef045a1d710000032": { "_id": {   "$id": "5197f4bef045a1d710000032" }, "tag": 5487, "serial": "1z5589ss56", "type": "soda can", "dept": "noc", "location": "mitchell", "date": 1368913086, "moves": null } 

i insert new document "moves".

i have been able once $set, subsequent $push nothing.

    <?php   $m = new mongo();  $d = $m->selectdb('peeps'); $c = $d->family; $fields = array('tag' => 5487 , 'serial' => '1z5589ss56', 'type' => 'soda can', 'dept' => 'noc', 'location' => 'mitchell', 'date' => time() );  $can = new asset($fields); #$c->save($can);  #update insert move  $c->update(array('_id' => new mongoid('5197f0cef045a1d710000032')), array('$push' => array('moves' => $can)));   $cur = $c->find(); $j = json_encode(iterator_to_array($cur)); print($j);   class asset{      public $tag;     public $serial;     public $type;     public $dept;     public $location;     public $date;     public $moves;      public function __construct($fields){         $this->tag = $fields['tag'];         $this->serial = $fields['serial'];         $this->type = $fields['type'];         $this->dept = $fields['dept'];         $this->location = $fields['location'];         $this->date = $fields['date'];     } } 

based on have read, should create nested document inside 5197f0cef045a1d710000032.moves every time reload page.

i not sure missing.

thanks,

mitchell

you should not using $set simple value if plan on later using $push same field.

use $push first time update also. create array of single element, , able add (push) more elements it.