php如何将mongodb中的时间戳字段转换成日期时间格式输出并分组？

可以使用project进行加工处理，代码如下：

<?php
$manager = new MongoDB\Driver\Manager("mongodb://localhost:27017");

// 插入数据
$bulk = new MongoDB\Driver\BulkWrite;

$bulk->insert(['x' => 2, 'name' => 'bfw', 'scores' => 123, 'atime' => time()-1000000]);
$bulk->insert(['x' => 2, 'name' => 'google', 'scores' => 10, 'atime' => time()-200000]);
$bulk->insert(['x' => 2, 'name' => 'baidu', 'scores' => 11, 'atime' => time()-1231123]);
$bulk->insert(['x' => 2, 'name' => 'bfw', 'scores' => 200, 'atime' => time()]);
$bulk->insert(['x' => 2, 'name' => 'bfw', 'scores' => 123, 'atime' => time()]);
$bulk->insert(['x' => 2, 'name' => 'google', 'scores' => 10, 'atime' => time()]);
$bulk->insert(['x' => 2, 'name' => 'baidu', 'scores' => 11, 'atime' => time()]);
$bulk->insert(['x' => 2, 'name' => 'bfw', 'scores' => 200, 'atime' => time()]);
$_data = $manager->executeBulkWrite('test.sites2', $bulk);


$utcdatetime = new MongoDB\BSON\UTCDateTime(0); //1970.01.01 00:00:00
$repair_time = 3600000 * 8; //修复时差
$param = [
    'aggregate' => 'sites2', //表名

    'pipeline' => [

        [
//完整的format格式是%Y-%m-%d %H:%M:%S:%L
            '$project' => [
                'datetime' => ['$dateToString' => ['format' => "%Y-%m-%d", 'date' => ['$add' => [$utcdatetime, ['$multiply' => ['$atime', 1000]], $repair_time]]]], "x" => '$x'

            ]],

        ['$match' => ['x' => 2]],
        ['$group' => ['_id' => '$datetime', 'count' => ['$sum' => 1]]],
    ],
    'cursor' => new \stdClass()// 高版本需要带上这个值
];
//除了$sum外还有$max最大值 $min最小值 $avg平均值

$command = new \MongoDB\Driver\Command($param);
$cursor = $manager->executeCommand('test', $command);


foreach ($cursor as $document) {
    $document = objectToArray($document);
    print_r($document);
}

function objectToArray($object) {
    $result = array();
    $object = is_object($object) ? get_object_vars($object) : $object;
    foreach ($object as $key => $val) {
        $val = (is_object($val) || is_array($val)) ? objectToArray($val) : $val;
        $result[$key] = $val;
    }
    return $result;
}