Unknown error executing command (empty document returned), when executing aggregate in mongodb using php -


i want group in mongodb: code below:

$m = new mongoclient("localhost"); $c = $m->selectdb("grl_db")->selectcollection("user_tbl"); $data = array (     'title' => 'this title',     'author' => 'bob',     'posted' => new mongodate,     'pageviews' => 5,     'tags' => array ( 'fun', 'good', 'fun' ),     'comments' => array (       array (         'author' => 'joe',         'text' => 'this cool',       ),       array (         'author' => 'sam',         'text' => 'this bad',       ),     ),     'other' =>array (       'foo' => 5,     ), ); $d = $c->insert($data, array("w" => 1));  $ops = array(     array(         '$project' => array(             "author" => 1,             "tags"   => 1,         )     ),     array('$unwind' => '$tags'),     array(         '$group' => array(             "_id" => array("tags" => '$tags'),             "authors" => array('$addtoset' => '$author'),         ),     ), ); $results = $c->aggregate($ops); 

but err occurs:

type: mongoresultexception

message: unknown error executing command (empty document returned)

filename: d:\projects\sns\grl1.0\trunk\src\server\grl\application\models\user_model.php

line number: 195

how can solve problem. please me!!!

the problem php version. aggregate, php version on 5.6.1 think php version may below 5.6. please use xampp higher version.


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