ding_event.install

<?php
/**
 * @file
 * Update functions for the ding_event module.
 */

/**
 * Implements hook_update_N().
 *
 * Add end date to the field.
 */
function ding_event_update_7001(&$sandbox) {
  return date_field_update_add_end_date('field_event_date');
}

/**
 * Helper function.
 *
 * Allows to update a date field (without deleting existing content) to allow
 * input of an end date.
 *
 * @param string $field_name
 *   machine name of the field to be updated.
 *
 * @return string
 *   Message that will be show when update is finished.
 */
function date_field_update_add_end_date($field_name) {
  $field_info = field_info_field($field_name);

  if (!$field_info) {
    return t('Field "@fld" doesn\'t exists. Update aborted.', array('@fld' => $field_name));
  }

  // Remove non-db settings.
  $non_db_settings = array(
    'field_name',
    'type',
    'module',
    'active',
    'locked',
    'cardinality',
    'deleted',
    'columns',
    'bundles',
  );

  $to_column = $field_info['columns']['value'];
  foreach ($non_db_settings as $setting) {
    unset($field_info[$setting]);
  }
  unset($field_info['storage']['details']);

  // Add end date setting.
  $field_info['settings']['todate'] = 'optional';
  $update_ok = db_update('field_config')
      ->fields(array('data' => serialize($field_info)))
      ->condition('field_name', $field_name)
      ->execute();

  // Alter field value storage tables (data and revisions).
  $field_data_table = 'field_data_' . $field_name;
  $field_rev_table = 'field_revision_' . $field_name;
  $field = $field_name . '_value2';
  db_add_field($field_data_table, $field, $to_column);
  db_add_field($field_rev_table, $field, $to_column);

  if ($update_ok && db_field_exists($field_data_table, $field) && db_field_exists($field_rev_table, $field)) {
    // Set default value for "to" date that equals "from".
    db_update($field_data_table)->expression($field, $field_name . '_value')->execute();
    db_update($field_rev_table)->expression($field, $field_name . '_value')->execute();
    cache_clear_all();
    return t('Field "@fld" updated successfully', array('@fld' => $field_name));
  }
  else {
    return t('Update failed!');
  }
}