HHVM MongoDb聚合似乎不起作用(HHVM MongoDb aggregation seems like it doesn't work)

 我在hhvm上运行了一些php脚本我试图从MongoDB 3.2中的我的集合中获取数值字段的最大值这是我的聚合管道 
 
    $mongo = new \MongoDB\Driver\Manager(MONGODB_HOST);
    $myCollection = new \MongoDB\Collection($mongo, "mydb.mycollection");

    $pipeline = [
            [
                '$group' => [
                    '_id' => 'group_field',
                    'slId' => ['$max' => '$saleId']
                ],
            ]
        ];

    $doc = $myCollection->aggregate($pipeline);
 
 这个管道完全适用于mongo shell，但是从php $ doc包含我的集合中的所有文档，没有$ group应用于它们也许有人可以帮助我吗？ 

I have some php script running on hhvm I'm trying to get max value of numeric field from my collection in MongoDB 3.2 Here is my aggregation pipeline
 
    $mongo = new \MongoDB\Driver\Manager(MONGODB_HOST);
    $myCollection = new \MongoDB\Collection($mongo, "mydb.mycollection");

    $pipeline = [
            [
                '$group' => [
                    '_id' => 'group_field',
                    'slId' => ['$max' => '$saleId']
                ],
            ]
        ];

    $doc = $myCollection->aggregate($pipeline);
 
This pipeline perfectly works in mongo shell, but from php $doc contains all documents from my collection and no $group is applied to them Maybe someone can help me with that?

原文：https://stackoverflow.com/questions/35081494