Weird auto increment issue - php

Question

I am making a transaction table with an auto increment field of BIGINT(20).
When a new transaction is added, the insert Id is retrieved and formatted to be more readable:
public function add_transaction($paymethod, $cursus_id)
{
$this->load->model('Config_model');
$btw = $this->Config_model->get('transactions.btw');
$query = " INSERT INTO transacties(userid, paymethod, amount, btw_pc)
VALUES((SELECT userid FROM users WHERE lcase(username)=lcase('{$this->session->userdata('username')}')),
'{$paymethod}',
(SELECT prijs FROM p_cursus_uitvoering WHERE uitvoering_id = {$cursus_id}),
{$btw});";
$this->db->query($query);
$insertId = $this->db->insert_id();
$newCode = date('Ymd') . str_pad($insertId, 8, '0', STR_PAD_LEFT);
$this->db->where('transact_id', $insertId);
$this->db->update('transacties', ['transact_id' => $newCode]);
return $newCode;
}
The result is that the ID get updated from eg: 5 to 2015041800000005.
This is working perfectly, but as you can see, the newCode is returned in the function and used by another function where it's reinserted in another table.
Here is where the problem arises, the ID turns into: 201504192058506757.
Even when I echo the newCode, it still prints 201504192058506757.. even though it is inserted correctly once, but incorrectly the second time!
EDIT:
Here is the code snippet in which the function is called:
public function workshop(){
$this->load->model('Inschrijven_model');
$paymethod = $this->input->post("paymethod");
//eigenlijk uitvoering_id.....
$cursus_id = $this->input->post("cursus_id");
if($paymethod == null || $cursus_id == null){
redirect('cursus');
}
if($this->Inschrijven_model->cursus_has_room($cursus_id)){
if(!$this->Inschrijven_model->cursus_ingeschreven($cursus_id)){
$this->load->model('Cc_payment_model');
$this->load->model('Cursus_model');
$amount = $this->Cursus_model->get_price($cursus_id);
$orderId = $this->Cc_payment_model->add_transaction($paymethod, $cursus_id);
$this->Inschrijven_model->cursus_inschrijven($cursus_id,$orderId);
$function = explode('_',$paymethod);
$this->{$function[0]}($function[1], $amount, $orderId);
}else{
echo "Al ingeschreven";
}
}else{
echo "geen ruimte";
}
}
And here is the code snippet in which the return $newCode is being reinserted:
public function cursus_inschrijven($cursus_id,$transaction_id){
$query = " INSERT INTO p_cursus_in(uitvoering_id, userid, transact_id)
VALUES({$cursus_id},(SELECT userid FROM users WHERE lcase(username)=lcase('{$this->session->userdata('username')}')),{$transaction_id})";
$this->db->query($query);
}
It is reinserted so I can make a connection between someone's registration into a class and their payment for that class.

Answer 1

You have to convert the BIGINT to string before you get it into PHP
Here's how you can convert it with a SQL statement:
https://dev.mysql.com/doc/refman/5.7/en/cast-functions.html#function_convert
I don't know what framework you're using but you have to do a conversion if you're using BIGINT whose length is not supported by PHP directly. It seems that the framework will read the record after updated to check if the operation's done successfully, and because of the process of reading without the conversion, you got a wrong number.
You can also use PHP GMP module to handle BIGINT:
https://php.net/manual/en/book.gmp.php