protected function createIndexName($type, array $columns)
{
$short_type = ['primary' => 'pk', 'foreign' => 'fk', 'unique' => 'uk'];
$type = isset($short_type[$type]) ? $short_type[$type] : $type;
$index = strtolower($this->prefix . $this->table . '_' . implode('_', $columns) . '_' . $type);
// max index name length is 30 chars
return substr(str_replace(['-', '.'], '_', $index), 0, 30);
}