如何使用TCPDF，PHP和SQL将所有id导出为PDF格式的条形码

I'm trying to print results from sql query to barcode and pdf using TCPDF.

How would i print all this to BARCODE in PDF using TCPDF? I tryed using examples but i always get headers already sent error when i try to include db connection class...

<div id="printAllthis">
<?php
$entry = $db->odradi("SELECT * FROM customers ORDER BY id_number ASC"); 
if (!empty($entry)) {
    foreach($entry as $data=>$value){ 
        ?><div class="col-xs-12 col-sm-4 col-lg-2">
            <?php echo $entry[$data]['id_number'] ?>
          </div>
    <?php } } ?>
</div>