//查询条件
        $filter=[];
        //当需要分页显示，排序，和忽略字段
        $options = [
            'skip'=>($page - 1) * $pageSize,
            'limit'=>$pageSize,
            'sort' => ['createTime' => -1],
            'projection'=>['_id'=> False],
        ];
        $query = new MongoDB\Driver\Query($filter, $options); 
       $command = new MongoDB\Driver\Command(
            array(
                "count" => '集合名',
                "query" => $query,
            )
        );
        $count = $this->mongoManger->executeCommand(‘数据库名’,$command)->toArray()[0]->n;
        var_dump($count);