mongodb php语法项目字段有条件

Question

我有此查询，它为两个日期字段不相等的每个事件数组元素返回_id。在mongo客户端中可以正常工作：

db.endUsers.aggregate([{$match:{'events':{$elemMatch:{'lastinvitedate":{$exists:true},"originalinvitedate":{$exists:true},}}}},{$unwind: "$events"},{$match: {'events.lastinvitedate":{$exists:true},"events.originalinvitedate":{$exists:true},}},{$project: { eventid: { $cond: { if : { $ne: ['$events.lastinvitedate', $events.originalinvitedate' ] }, then:'$events._id', else: 0}}}},{$redact: {$cond: {if: { $eq: [ "$eventid", 0 ] },then: '$$PRUNE',else: '$$DESCEND'}}}])

当我用php编写时没有任何结果

$pipeline = [

        ['$match' => [
            'events' => [
                '$elemMatch' => [
                    'lastinvitedate' => ['$exists' => true],
                    'originalinvitedate' => ['$exists' => true],
                    ],
                ]
            ]
        ],

        ['$unwind' => '$events'],

        ['$match' => [
                'events.lastinvitedate' => ['$exists' => true],
                'events.originalinvitedate' => ['$exists' => true],
            ]
        ],

        ['$project' => [
                'eventId' => [ '$cond' =>
                    [ 'if' =>
                        [ '$ne' =>
                            ['$events.originalinvitedate', '$events.lastinvitedate' ]
                        ],
                    'then' => '$events._id',
                    'else' => 0
                    ]
                ],
            ]
        ],
        [ '$redact' => [ '$cond' =>
                [ 'if' =>
                    [ '$eq' =>
                        [ '$eventid', 0 ]
                    ],
                    'then' => '$$PRUNE',
                    'else' => '$$DESCEND'
                ]
            ]
        ]
    ];

任何线索为何？ 谢谢