我想加入两个集合并对外部表中的日期字段进行排序，然后对这些字段进行分组以从每个设备的最近日期仅获取一条记录，如下所示

 $collection = $this->db->dv_device;

        $result_data =  $collection->aggregate(
            array('$lookup'=>array('from'=>'dv_device_readings', 'localField'=>'device_id', 'foreignField'=>'device_id','as'=>'result_data')),
            array('$match'=>array('user_id'=>'5809c169622d10a419000029')),
            array('$sort'=>array('result_data.date_time'=>-1)),
            array('$group' => array(
            "_id" => array("device_id" => '$result_data.device_id'),
            "device_id" => array('$first' => '$result_data.device_id'),
            "date_time" => array('$first' => '$result_data.date_time'),
            "dc_voltage" => array('$first' => '$result_data.dc_voltage'),
            "dc_current" => array('$first' => '$result_data.dc_current'),
            "output_voltage" => array('$first' => '$result_data.output_voltage'),
            "output_current" => array('$first' => '$result_data.output_current'),
        ))
        );

通过在 php 中使用上面的代码，我得到了以下结果，加入两个集合工作正常，但排序和分组不起作用。

Array
(
    [waitedMS] => 0
    [result] => Array
        (
            [0] => Array
                (
                    [_id] => Array
                        (
                            [device_id] => Array
                                (
                                    [0] => dv1002
                                    [1] => dv1002
                                )

                        )

                    [device_id] => Array
                        (
                            [0] => dv1002
                            [1] => dv1002
                        )

                    [date_time] => Array
                        (
                            [0] => MongoDate Object
                                (
                                    [sec] => 1477476049
                                    [usec] => 0
                                )

                            [1] => MongoDate Object
                                (
                                    [sec] => 1477476313
                                    [usec] => 0
                                )

                        )

                    [dc_voltage] => Array
                        (
                            [0] => dv1
                            [1] => dvv2
                        )

                    [dc_current] => Array
                        (
                            [0] => dc1
                            [1] => dc2
                        )

                    [output_voltage] => Array
                        (
                            [0] => output voltage1
                            [1] => output voltage2
                        )

                    [output_current] => Array
                        (
                            [0] => output current1
                            [1] => output current2
                        )


                )

        )

    [ok] => 1
)

我需要如下结果

Array
(
    [waitedMS] => 0
    [result] => Array
        (
            [0] => Array
                (

                    [device_id] => dv1002

                    [date_time] => MongoDate Object
                                (
                                    [sec] => 1477476313
                                    [usec] => 0
                                )
                    [dc_voltage] => dvv2
                    [dc_current] => dc2
                    [output_voltage] => output voltage2
                    [output_current] => output current2

                )

        )

    [ok] => 1
)

最佳答案

您可能需要一个 $unwind ，因此您可以对查找的集合进行分组。在 $match 之后添加此行.

array('$unwind'=>'$result_data')

关于php - 如何在mongodb中对查找结果进行排序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40263052/