Marko Bischof

 
public function beforeValidate()
{
    if (!empty($this->firstname)) {
        $this->validatorList->add(Yii::createComponent(
            'class' => 'CRequiredValidator',
            'attributes' => array('lastname'),
            'message' => 'Das Feld {attribute} muss eingegeben werden',
        ));
    }
 
    return parent::beforeValidate();
}