Generating Unique ID

[eluser]Michael Wales[/eluser]
You'll never be able to guarantee absolute uniqueness on the insertion by generating a hash and then substringing it. It will be pretty unique - but never guaranteed.

Personally, I would just use the string helper, then loop until the query is properly executed.

Code:

function make_unique($filename = NULL) {
  if ($filename !== NULL) {
    $this->load->helper('string');
    $unique = FALSE;
    while ($unique === FALSE) {
      if ($this->db->update('files', array('id' => random_string('alnum', 5)), array('filename' => $filename))) {
        $unique = TRUE;
      }
    }
    return TRUE;
  }
  return FALSE;
}

Then just set that field as a UNIQUE key within your database engine (or even a primary, since it's the identifier). You don't have to use random_string - hashing time() and then substringing it would work, but you still need a fall-back due to the chance of nonuniqueness.