validation: model related with other models

model

class Model_Core_Account extends Abstract_Model_Base {

  public $list_fields = array();

  public function check()
  {
    // validate list fields if exist, here!

    // call parent model validation
    return parent::check();
  }


class Controller_API_Accounts extends Controller_API {

  public function post_collection()
  {
     $account = new ...
     $account->list_fields = arr::get($this->_request_body, 'fields', array());