multiple student registration at same time without data conflict in Codeigniter - php

Question

I am working on an application built with codeigniter that used to register students. It was working fine till date but yesterday multiple students try to register at same instance, then data was conflicted and entered wrong data into database.
what should I do to prevent this. I have used following code.
public function sregister()
{
if (!$_SERVER['HTTP_REFERER']) redirect(base_url(), 'refresh');
$query1 = $this->db->query("SELECT MAX(right(ref,3)) AS `maxid` FROM p2 WHERE ref LIKE '" . date('Ymd') . "%'")->row()->maxid;
$p2data['name'] = $this->input->post('pname');
$p2data['fname'] = $this->input->post('pfname');
$p2data['mname'] = $this->input->post('pmname');
$p2data['dob'] = date('m/d/Y', strtotime($this->input->post('pdob')));
$p2data['category'] = $this->input->post('pcategory');
$p2data['gender'] = $this->input->post('pgender');
$p2data['nationality'] = $this->input->post('pnationality');
$p2data['marital'] = $this->input->post('pmarital');
$p2data['ref'] = date('Ymd') . sprintf('%03d', ($query1 + 1));
$this->db->insert('p2', $p2data);
}

Answer 1

You can use commit and roll back statements in codeigniter to prevent this.
Begin a transaction and when the status is true, commit the changes or else roll back to initial. This prevents any inconsistency in the database.
Example:
$this->db->trans_begin();
$this->db->query('QUERY1');
$this->db->query('QUERY2');
$this->db->query('QUERY3');
if ($this->db->trans_status() === FALSE){
$this->db->trans_rollback();
}else{
$this->db->trans_commit();
}
Or you can refer :https://codeigniter.com/user_guide/database/transactions.html

Answer 2

This is a classic (and fortunately easily avoidable, even without transactions) race condition.
Instead of determining by yourself what the next ID must be, you should have some sort of auto-increment do the hard work for you.
If the ref field you're calculating is the main index for the table, just run an alter on the table and set it to auto-increment. Then, do not insert anything on that field, just fill the others, like this:
public function sregister()
{
if (!$_SERVER['HTTP_REFERER']) redirect(base_url(), 'refresh');
$query1 = $this->db->query("SELECT MAX(right(ref,3)) AS `maxid` FROM p2 WHERE ref LIKE '" . date('Ymd') . "%'")->row()->maxid;
$p2data['name'] = $this->input->post('pname');
$p2data['fname'] = $this->input->post('pfname');
$p2data['mname'] = $this->input->post('pmname');
$p2data['dob'] = date('m/d/Y', strtotime($this->input->post('pdob')));
$p2data['category'] = $this->input->post('pcategory');
$p2data['gender'] = $this->input->post('pgender');
$p2data['nationality'] = $this->input->post('pnationality');
$p2data['marital'] = $this->input->post('pmarital');
$this->db->insert('p2', $p2data);
return $this->db->insert_id();
}
a successful insert will return the Insertion ID, which is nothing more than the value of the table's auto-increment field for the row you just inserted.