protected function merge_association_options($options)
{
$available_options = array_merge(self::$valid_association_options, static::$valid_association_options);
$valid_options = array_intersect_key(array_flip($available_options), $options);
foreach ($valid_options as $option => $v) {
$valid_options[$option] = $options[$option];
}
return $valid_options;
}