Validate form but not subform - php

Question

I have a Zend_Form whose sub-form is only required in certain circumstances. The parent form and the sub-form both have required fields. The sub-form will not always be filled but when any of its elements are filled, they should all be filled.
<?php
class Cred extends Zend_Form
{
public function init()
{
$title = new Zend_Form_Element_Text('Title');
$title->setLabel('Title')
->setRequired(TRUE);
$this->addElement($title);
$award = new Zend_Form_Element_Text('Awarded');
$award->setLabel('Awarded On')
->setRequired(TRUE)
->addValidator('date');
$this->addElement($award);
$subform = new Zend_Form_SubForm();
$proof = new Zend_Form_Element_File('Documentation');
$proof->setLabel('Documentation')
->setRequired(TRUE)
->addValidator('Size', false, 409600) // limit to 400K
->addValidator('Extension', false, 'pdf');
$subform->addElement($proof);
$lang = new Zend_Form_Element_Select('Language');
$lang->setLabel('Language')->setRequired(TRUE);
$subform->addElement($lang);
$this->addSubForm($subform,'importForm');
$submit = new Zend_Form_Element_Submit('submitForm');
$submit->setLabel('Save');
$this->addElement($submit);
$this->setAction('/cred/save')
->setMethod('post')
->setEnctype(Zend_Form::ENCTYPE_MULTIPART);
}
}
When I call $form->isValid($_POST), it validates both the parent form and the sub-form and returns errors when the subform's required elements are empty even when the sub-form itself is not required.
Other than overloading the isValid() function, is there any way to validate only the parent form?

Answer 1

If you look into the source code the isValid() method of Zend_Form you see that there is no explicit mechanism that prevents the execution of the validators on the subforms (line 2273 ff).
Anyway, If I understand your requirement "The sub-form will not always be filled but when any of its elements are filled, they should all be filled." correctly then I think your problem does not necessarily have something to do with subforms per se but rather with conditional validation. This can be solved pretty easy with a custom validator: How to validate either Zend_Form_Element_File or Zend_Form_Element_Text are not empty.
Just keep in mind that the elements in $context contain only the subform elements.