public function rules()
{
  // NOTE: you should only define rules for those attributes that
  // will receive user inputs.
  return array(
    array('start, end', 'required'),
    array('user_id', 'numerical', 'integerOnly'=>true),
    array('timestamp','default','value'=>date('Y-m-d H:i:s')),
    // The following rule is used by search().
    // Please remove those attributes that should not be searched.
    array('id, start, end, user_id, timestamp', 'safe', 'on'=>'search'),
  );
}

function beforeSave()
{
  $this->user_id = Yii::app()->user->id;
  return true;
}