mongo 聚合函数分组

Question

我是 mongodb 的新手，使用聚合函数来获取一些记录

我使用的查询是：

    $records = $this->raw()->aggregate([
                                            ['$match' =>  ["ts" => ['$gte'=>  $startTime,'$lt'=>  $endTime]]],
                                            ['$group' => ["_id" =>["config" => '$conf', "status" => '$s' ], "count" =>['$sum' =>1]],
                                                "ts" =>
                                                    [ 
                                                        '$dateToString' => 
                                                                            [ 
                                                                                'format' => '%Y-%m-%d', 
                                                                                'date' => $startTime, 
                                                                                'timezone' => '+05:30' 
                                                                            ] 
                                                    ] 
                                            ]
                                            ])->toArray();

它返回一个错误：管道阶段规范对象必须只包含一个字段。 请有人告诉我我的查询有什么问题。基本上我想在记录中存储日期。

编辑：与上面相同的代码

$records = $this->raw()->aggregate([
    [
        '$match' =>  ["ts" => [
                '$gte'=>  $startTime,
                '$lt'=>  $endTime
            ]
        ]
    ],
    [
        '$group' => [
            "_id" => [
                "config" => '$conf', 
                "status" => '$s' 
                ], 
            "count" => [
                '$sum' =>1
                ]
        ],
        "ts" => [ 
                '$dateToString' => 
                    [ 
                        'format' => '%Y-%m-%d', 
                        'date' => $startTime, 
                        'timezone' => '+05:30' 
                    ] 
            ] 
    ]
])->toArray();