Generating Unique Values for MySQL Unique Fields - php

Question

When a user signs up to my website, for example, I create a unique string of length 40 and insert it into the database. We then send an email to the newly signed up user containing this unique string in the form of an URL, and this all works fine.
But how do you create and insert this signup entity ensuring that the field with the unique property is actually unique?
My current approach is as follows:
$key = '';
$repeat = true;
while ($repeat) {
$key = generate_hash(40);
$is_unique = (count($model->get_by_key($key)) === 0) ? true : false;
$repeat = ($is_unique) ? false : true;
}
// At this point I know the key is unique and can insert it...
I am not happy with this code, as I try to avoid while loops in general. Is there a better way to achieve what I am doing here?
The bottom line is that the MySQL field containing these keys has the unique property and I need to know that no unique-violations will occur when inserting these keys.

Answer 1

Ok, basically you have two approaches.
Let the DB handle this and use UUID() to create a unique identifier that you can use in the emails.
According to your MySQL version you have some options:
A. With MySQL 4.1 and above you can use the function directly with INSERT INTO:
INSERT INTO table_name
(unique_id, field1, field2)
VALUES
(UUID(), "smth", "smth")
B. With MySQL 5.0 you can create a TRIGGER and have the unique field automatically filled upon insertion:
CREATE TRIGGER
unique_id
BEFORE INSERT ON
table_name
FOR EACH ROW
SET NEW.unique_id = UUID()
You can check programatically if the the generated id is really unique. The same you are doing now but you can refactor the code a little bit like so:
$key = generate_hash(40);
while ( count($model->get_by_key($key)) ) {
$key = generate_hash(40);
}
//here you have an unique id in $key

Answer 2

There are built in unique id functions in almost every language for that.In php,
echo uniqid();

Answer 3

You can generate 256^40 different 40-characters strings.
Sun will explode before you generate 2 identical strings.

Answer 4

You can use md5(time()) as your unique value instead. md5 of time wouldn't be same for each user submitting.
$time = time();
$md5 = md5($time);
As long as md5() just containing 32 string length, you can add an unique word after the md5().
$unique = $md5."uniq1234";
Now you have 40 unique string length. At last you can add $unique as your unique value in database

Answer 5

You can use this function to generate uniqueID ,
function keygen($length=10)
{
$key = '';
list($usec, $sec) = explode(' ', microtime());
mt_srand((float) $sec + ((float) $usec * 100000));
$inputs = array_merge(range('z','a'),range(0,9),range('A','Z'));
for($i=0; $i<$length; $i++)
{
$key .= $inputs{mt_rand(0,61)};
}
return $key;
}
echo keygen(10);