Create keys randomly with PHP - php

Question

I have an mobile app that request a key in my server, The key structure contains 7 characters as follows:
# + [0-9] + [0-9] + [0-9] + [A-Z] + [A-Z] + [0-9]
#876EU8, #668KI2 .......
Whereas the key initially has seven characters, in this case three numbers, two letters and one number, doing the math this gives a maximum of 676,000 keys.
To gerate this keys I'm using this code in PHP:
function generateRandomString($length = 2) {
$characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$charactersLength = strlen($characters);
$randomString = '';
for ($i = 0; $i < $length; $i++) {
$randomString .= $characters[rand(0, $charactersLength - 1)];
}
return $randomString;
}
$randomKeyNumber = rand(100,999);
$randomKeyLetter = generateRandomString();
$randomKeyLast = rand(0,9);
$randomKey = "#".$randomKeyNumber.$randomKeyLetter.$randomKeyLast;//Returns a key like #876TG9
The next code check if the key exists inside the database, If exists he random another key, if not he insert the key in database and return this key to my app
This code works perfectly, but assuming the system has already generated a total of 650,000 keys, in the case of this code it would always generate the same keys, and the likelihood of it generate a key that does not exist yet is very small.
How can I solve this problem and avoid future problems? (There is no problem in creating the keys in an orderly manner, eg 000AA0, 000AA1, 000AA2, 000AA3 .... 999ZZ9)

Answer 1

What you can do is make a PDO::query() to issue a SELECT COUNT(*) or simply a SELECT * statement with all the keys you already have added, and then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned (i.e. in this case, all of them)
This is a manual example
<?php
$sql = "SELECT COUNT(*) FROM Keys";
if ($res = $conn->query($sql)) {
/* Check the number of rows that match the SELECT statement */
if ($res->fetchColumn() > 0) {
/* Issue the real SELECT statement and work with the results */
$sql = "SELECT name FROM fruit WHERE calories > 100";
foreach ($conn->query($sql) as $row) {
print "Name: " . $row['NAME'] . "\n";
}
}
/* No rows matched -- do something else */
else {
print "No rows matched the query.";
}
}
$res = null;
$conn = null;
?>
This is the code you need for your case:
<?php
$sql = "SELECT * From Keys";
if ($res = $conn->query($sql)) {
/* Check the number of rows that match the SELECT statement */
if ($res->fetchColumn() > 0) {
/* and then you get the id of the last one on the list, and to that one you add 1 */
$last_id = $conn->lastInsertId();
$new_id = $last_id + 1;
/* then you insert that in some place inside the key itself, that way you don't need to worry than two keys can be equal */
}
else {
/* No rows matched, just create a key and add to the database here */
}
}
¿>
Alternatively you can make a query SELECT statement combined with the countRows in PDO, it doesn't work all the times in the portable apps and/or databases, but like we don't know more about your app we can't know if this is gonna work.
PS. Don't use rand(). Use mt_rand() instead. It is more efficient with the resources of the server ;)