An unsafe implementation of storing structured data in the Drupal 7 User data property

drupal7-unsafe-user-data.php

<?php
$user->data['employee'] = array(
  'employee_number' => 123456,
  'employee_details' => array(
    'salary' => 65000,
    'access_level' => 'A',
    'start_date' => 1425439660,
  ),
);
user_save($user);
 
// Get the users employee number.
$employee_number = !empty($user->data['employee']['employee_number']) ? $user->data['employee']['employee_number'] : FALSE;