如何使用php从mongodb读取数据

Question

我正在使用mongodb，而我的查找结果是这个

> db.analysis.find().pretty() 
{ "_id" : "a", "age" : [ "d" ] }
{ "_id" : "b", "age" : [ "a", "b", "e" ] }

这是我在php中使用的查询：

<?php

error_reporting(E_ALL);

ini_set("display_errors", 1);

$mng = new MongoDB\Driver\Manager("mongodb://localhost:27017");

$bulk = new MongoDB\Driver\BulkWrite;

$query = new MongoDB\Driver\Query([]);

$rows = $mng->executeQuery("whot.analysis", $query);

$return_array = array();

   foreach ($rows as $row) {
            array_push($return_array,
                 array(
                   "_id" => "$row->_id",
                   "age" => "$row->age"
            ));
           }

$json= json_encode($return_array);

echo $json;

结果

Notice: Array to string conversion in /usr/local/nginx/html/mongo_analysis.php on line 39

Notice: Array to string conversion in /usr/local/nginx/html/mongo_analysis.php on line 39

[{"_id":"a","age":"Array"},{"_id":"b","age":"Array"}]

任何人都可以让我知道如何更改代码吗？

我想将Array更改为字符串。