[PHP知识库]laravel、lumen导出大量数据到csv文件，运用PHP生成器功能

/**
     *
     *
     * 订单数据导出
     */
    public function export()
    {
        $where = [];
        $total = Order::where($where)->count();
        if ($total == 0) {
            return '无数据';
        }
        $title = ['订单号', '商品名称', '规格', '数量','订单价格','创建时间', '订单状态','收货人姓名','电话','省份','市区','区域','地址'];
        set_time_limit(0);
         //设置程序运行内存
        ini_set('memory_limit', '5M');
        $fileName = '订单信息统计'.date('Y-m-d');
        header('Content-Encoding: UTF-8');
        header("Content-type:application/vnd.ms-excel;charset=UTF-8");
        header('Content-Disposition: attachment;filename="' . $fileName . '.csv"');
         //打开文件
        $fp = fopen('php://output', 'a');
         //添加BOM头，以UTF8编码导出CSV文件，如果文件头未添加BOM头，打开会出现乱码。
        fwrite($fp, chr(0xEF).chr(0xBB).chr(0xBF));
         //数据写入csv文件
        fputcsv($fp, $title);
        $sqlLimit = 500;
        // DB::enableQueryLog();
        for($i = 0;$i < ceil($total/$sqlLimit);++$i){
            $lists = Db::table('orders as a')
            ->leftJoin('address_users as b','a.address_id' ,'=' ,'b.id')
            ->leftJoin('product_skus as c','a.sku_id','=','c.id')
            ->leftJoin('product_spus as d','c.product_id','=','d.id')
            ->where($where)
            ->select('a.order_no','d.title','c.attrbute_text','a.num','a.amount','a.created_at','a.status','b.name','b.mobile','b.province','b.city','b.area','b.address')
            ->forPage($i,$sqlLimit)
            ->get()
            ->map(function ($value) {
                $value->status = $this->orderStatus[$value->status];
                return $value;
            });
            ##yield引入
            $lists = self::yieldData($lists);
            foreach($lists as $r) {
                //数据写入csv文件
                $r->order_no = "\t".$r->order_no;
                fputcsv($fp, (array)$r);
            }
            //数据从PHP的缓冲中释放出来
            ob_flush();
             // 被释放出来的数据发送到浏览器
            flush();
        }
    }

    public static function yieldData($data)
    {
        foreach ($data as $datum){
            yield $datum;
        }
    }