Zend Framework generate unique string

Question

I want to generate a unique 4-6 char long AlphaNumeric string to save in db with each record(user). The db field has a unique index, so trying to save a pre-existing string generates an error. Right now I am generating a random string and using try-catch, so when adding a new record if it throws an exception, I generate another random string and attempt to save again, and the code keep trying until it adds a record successfully. This whole solution not only looks heavy but also ugly, so I want to change it. I am interested in an elegant solution, so any help/guidance is welcome.

Possible dupe stackoverflow.com/questions/6826106/generate-random-string — JohnD
– JohnD, Commented Sep 17, 2011 at 21:10
This may be related: stackoverflow.com/questions/7194506/… — Arnaud Le Blanc
– Arnaud Le Blanc, Commented Sep 17, 2011 at 21:11
@JohnD i know how to generate random strings, but the main issue is to add the approach to elegantly 1) generate the string in zend framework and 2) make sure the random string in unique in the database, and if it already exist, generate a new one until it found a unique string — Bryan
– Bryan, Commented Sep 17, 2011 at 21:18
As it's already indexed, you could (for the moment) generate N keys and then run a select query prior inserting. You could then find out in one round-trip which keys have been already consumed and then go on with the unused ones try-and-error again. Not really a solution, but I don't find the related question I'm looking for. — hakre
– hakre, Commented Sep 17, 2011 at 21:19
what is this random string for? Is it a string that some user will have to enter manually? Does it has to be 4-6 characters long? What happens if you run out of bits (ie. when all possible combinations has been generated)? — Yanick Rochon
– Yanick Rochon, Commented Sep 17, 2011 at 21:23

Community · Accepted Answer · 2017-05-23 10:24:35Z

6

With the given information :

id must be unique
id must not be numeric
id must not represent a sequential series
id will not be input by the user

The PHP function uniqid is exactly what you need. Though it returns a 13 character long hexadecimal value.

** Edit **

Yes, uniqid will return a seamingly sequential number, but we can get around this easily. Consider this code

class IDGenerator {
   //const BIT_MASK = '01110011';

   static public function generate() {

      $id = uniqid();

      $id = base_convert($id, 16, 2);
      $id = str_pad($id, strlen($id) + (8 - (strlen($id) % 8)), '0', STR_PAD_LEFT);

      $chunks = str_split($id, 8);
      //$mask = (int) base_convert(IDGenerator::BIT_MASK, 2, 10);

      $id = array();
      foreach ($chunks as $key => $chunk) {
         //$chunk = str_pad(base_convert(base_convert($chunk, 2, 10) ^ $mask, 10, 2), 8, '0', STR_PAD_LEFT);
         if ($key & 1) {  // odd
            array_unshift($id, $chunk);
         } else {         // even
            array_push($id, $chunk);
         }
      }

      return base_convert(implode($id), 2, 36);
   }
}

echo IDGenerator::generate();

Which will give results like

ivpa493xrx7
d173barerui
evpoiyjdryd
99ej19mnau2

Since there is nothing added or modified, except shuffling the bits around, there should not be any duplicated values and everything seems random. Voilà!

Update (2014-02-24)

I update this piece of code since the time it was originally posted. You may find the revised version here

edited May 23, 2017 at 10:24

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answered Sep 17, 2011 at 22:28

Yanick Rochon

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1 Comment

Bryan Over a year ago

but the value generated by uniqid are in sequence, though getting two adjacent values is very difficult, but values are in sequence.

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