PHP - generate serial number - php

Question

Can someone tell me if there's a better way doing this?
I am trying to generate a Serial number (function Taken from a Post on
this site )
Check in my database if this Serial exist, if it does,regenerate another
Insert Unique serial into Db
function GenerateSerial() {
$chars = array(0,1,2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z');
$sn = '';
$max = count($chars)-1;
for($i=0;$i<20;$i++){
$sn .= (!($i % 5) && $i ? '-' : '').$chars[rand(0, $max)];
}
return $sn;
}
// Generate SN
$serial = GenerateSerial() ;
// Check if it exists, then re-generate
function checkifSerialexist () {
$statement = $dbh->prepare("SELECT `id` FROM `table` WHERE `SN` = :existSN");
$statement->bindParam(':existSN', $serial, PDO::PARAM_STR);
$statement->execute();
$statement->setFetchMode(PDO::FETCH_ASSOC);
$result = $statement->fetchAll();
$serial_count = $statement->rowCount();
if ($serial_count > 0) {
$serial = GenerateSerial() ;
}
return $serial ;
}
//Now insert unique SN
$stmt = $dbh->prepare("INSERT INTO `table` (SN) VALUES (:sn)");
$stmt->bindParam(':sn', $serial, PDO::PARAM_STR);
ect....

Answer 1

You are not calling your checkifSerialexist() function nor are you sending the serial (and the database connection...) as a parameter.
It should be something like:
$serial = GenerateSerial() ;
while (checkifSerialexist($dbh, $serial))
{
$serial = GenerateSerial() ;
}
function checkifSerialexist ($dbh, $serial)
{
$statement = $dbh->prepare("SELECT `id` FROM `table` WHERE `SN` = :existSN");
$statement->bindParam(':existSN', $serial, PDO::PARAM_STR);
$statement->execute();
$statement->setFetchMode(PDO::FETCH_ASSOC);
$result = $statement->fetchAll();
return (count($result) > 0);
}

Answer 2

it's hard to say with the provided code, but my usual logic for unique generation is as follows:
$serial = genSerial();
while(!serialUnique($serial)) {
$serial = genSerial();
}
save($serial);
i always make my check functions (e.g. serialUnique) return a boolean.

Answer 3

It seems like your function that checks if the serial exists does not have the serial you generated earlier.
Depending on where your function is, it might not have access to the variable. Pass it as a parameter and return true or false from the checkIfSerialExists function.
function checkifSerialexist ($serial) {
$statement = $dbh->prepare("SELECT `id` FROM `table` WHERE `SN` = :existSN");
$statement->bindParam(':existSN', $serial, PDO::PARAM_STR);
$statement->execute();
$statement->setFetchMode(PDO::FETCH_ASSOC);
$result = $statement->fetchAll();
$serial_count = $statement->rowCount();
if ($serial_count > 0) {
return true;
} else {
return false;
}
}
Then from where you want to add it to the database, do something like
$serial = GenerateSerial() ;
if(checkifSerialexist($serial)) {
//Now insert unique SN
$stmt = $dbh->prepare("INSERT INTO `table` (SN) VALUES (:sn)");
$stmt->bindParam(':sn', $serial, PDO::PARAM_STR);
//ect....
}

Answer 4

echo implode('-', str_split(substr(strtoupper(md5(microtime().rand(1000, 9999))), 0, 20), 5));

Answer 5

this is just the simply way, you can apply more secure if you need, you can use sha1(), microtime() combined with anothers functions and unique user data, and check if serial generated exsists in your data base... litle bit more secure, like:
$user_mail = 'customer#domain.com';
function salt($leng = 22) {
return substr(sha1(mt_rand()), 0, $leng);
}
function serial(){
$hash = md5($user_mail . salt());
for ($i = 0; $i < 1000; $i++) {
$hash = md5($hash);
}
return implode('-', str_split(substr(strtoupper($hash), 0, 20), 5))
}
This exit: XXXX-XXXX-XXXX-XXXX serial pattern