private function _convertToArray($param)
{
$ret = array();
foreach ($param as $k => $v) {
if ($v instanceof PPModel) {
$ret[$k] = $v->toArray();
} else {
if (is_array($v)) {
$ret[$k] = $this->_convertToArray($v);
} else {
$ret[$k] = $v;
}
}
}
return $ret;
}