Drupal - Feeds Tamper - Legacy Import ID Swap

legacy.php

<?php

/**
 * When migrating Drupal sites using Feeds sometimes you'll need to re-map entity relationships.
 * When importing User Accounts, I always save the legacy UID from the old system.
 * Then while importing data that needs to re-map to the UID, I load it the legacy UID from the CSV,
 * then swap it out with the newley created ID using Feeds Tamper PHP.
 */

if (!empty($field)) {

    $query = new EntityFieldQuery();
    $query->entityCondition('entity_type', 'user')
        ->entityCondition('bundle', 'user')
        ->fieldCondition('field_legacy_id', 'value', $field, '=');

    $result = $query->execute();
    if (isset($result['user'])) {
        $user = array_shift($result['user']);
        return $user->uid;
    }
}