What's the cleanest way to get a checksum of a multidimensional array?

Question

I am doing some sql caching of certain queries. I'm using CakePHP so the query conditions are in an array thus:

array (
  0 => 
  array (
    0 => 'Tutorial.id IN ( SELECT tutorial_id FROM classifications WHERE classifications.product_id = 1 ) ',
  ),
  1 => 
  array (
    'Tutorial.status_id ' => 
    array (
      0 => 4,
      1 => 7,
    ),
  ),
  'OR' => 
  array (
    'Tutorial.user_id' => '40',
  ),
);

I'm mostly looking for the product_id, but there are some other possible conditions, so I wanted to reduce the array to a checksum and append it to the name of the cache file. This way I'd have tutorials_by_classification-413a86af or something, and I wouldn't have to pick thru the array.

I've seen the function to implode mutli-d arrays on php.net in the comments, but I'm wondering if there's a simpler way to achieve my goal.

Answer 1

How about serialize and md5? serialize creates a string representation of your array; md5 creates a hash of it.

Example:

$query = array (
  0 => 
  array (
    0 => 'Tutorial.id IN ( SELECT tutorial_id FROM classifications WHERE classifications.product_id = 1 ) ',
  ),
  1 => 
  array (
    'Tutorial.status_id ' => 
    array (
      0 => 4,
      1 => 7,
    ),
  ),
  'OR' => 
  array (
    'Tutorial.user_id' => '40',
  ),
);

$query_string = serialize($query);
$hash = md5($query_string);

echo $query_string, "\n\n\n", $hash, "\n";

/*
a:3:{i:0;a:1:{i:0;s:96:"Tutorial.id IN ( SELECT tutorial_id FROM classifications WHERE classifications.product_id = 1 ) ";}i:1;a:1:{s:19:"Tutorial.status_id ";a:2:{i:0;i:4;i:1;i:7;}}s:2:"OR";a:1:{s:16:"Tutorial.user_id";s:2:"40";}}


a5cb59f0ee259961e426c7ce9b7b8f32
*/

Answer 2

I would just do this:

$checksum = md5(json_encode($array));

json_encode is slightly faster than serialize, but you lose some of the benefits of serialize. However, for what you're doing, that doesn't matter.