PHP / Mongo DB : How to sort by a specific array attribute

Sorting in mongodb with .sort() only refers to sorting the documents themselves, not the values inside an array that are nested within those documents. With this schema, you will need to fetch the document and sort the values inside the array on the client side.

Thank you.

I found a work around with map/reduce, that works well for this case.

I put it here in case someone else is interrested :

//
//$folder_Id is the _id of the folder I want to list 
//map function
$mapFunc="function() {
                    var myFolder='". $folder_Id ."';
                    var obj = { // all the elements I need!
                        'Folders': {},
                        'Flds': {},
                        'Crea': {},
                        'TechInfo': {},
                        'Thumbs': {},
                        '_id': null,
                        'Order': null
                    }
                    if (this.Folders)obj.Folders = this.Folders ;
                    if (this.Flds)obj.Flds = this.Flds ;
                    if (this.Crea)obj.Crea = this.Crea ;
                    if (this.TechInfo)obj.TechInfo = this.TechInfo ;
                    if (this.Thumbs)obj.Thumbs = this.Thumbs ;
                    obj._id = this._id ;
                    if (this.Folders) {
                        for(var i=0 ; i< this.Folders.length ;i++){
                            if(this.Folders[i].F_id==myFolder){
                                obj.Order=  this.Folders[i].Ord
                                break;
                            }
                        }
                    }
                    emit( this._id , obj);
                }
        ";

//reduce function
$reduceFunc="function(key, values) {
                    values['_id']=key;
                    return  values  ;
                }
            ";


$mapReduceColl="MR_" . new MongoId();
$command = array(
    'mapreduce' => "File"
    ,'map' => $mapFunc
    ,'reduce' => $reduceFunc
    ,'query' => $query
    //,"verbose"=>true
    ,"out"=>array("replace"=>$mapReduceColl)
);
$statsInfo =  $db->MyDB->command($command);
$statsCollection =  $db->MyDB->selectCollection($statsInfo['result']);
$cursor = $statsCollection->find()->sort(array( $params["ordBy"]=>$params["ordByDir"]))->skip( $skip )->limit(  $nbreParPage );