Recently at work we came across an issue using Zend Frameworks Form builder – Zend Form. We were creating a form which contained a checkbox and this checkbox had to be checked for the form to be valid. In other words, if the checkbox wasn’t checked, the form should fail validation. Simple Eh?

This sounds easy, and our initial reaction was to use the setRequired() method, as seen in the example below.

Source code

1. $objForm = new Zend_Form();
2.  
3. $objForm->setMethod('post');
4.  
5. $objCheck = $objForm->createElement('checkbox', 'test')
6.                     ->setRequired(true);
7.  
8. $objForm->addElement($objCheck);

Bizarrely, this didn’t do the trick, and the form validation result would be valid even when the checkbox wasn’t checked. After doing a little research, we found the path to the answer on the Zend Framework issue tracker. This dilema is in part due to the way Zend Form uses  Zend_Validate_NotEmpty as a validator to check for an empty value, when an element is marked as Required. By default, the Zend Form Checkbox Element has these 2 properties in its core class:

Source code

1. /**
2.  * Value when not checked
3.  * @var string
4.  */
5. protected $_uncheckedValue = '0';
6.  
7. /**
8.  * Current value
9.  * @var string 0 or 1
10.   */
11. protected $_value = '0';

As you can see, the Zend Form Checkbox element by default has a value of ‘0‘, which is encased by quotes to make it a string rather than an integer. It is then passed through Zend_Validate_NotEmpty, and is validated by the following lines of code;

Source code

1. if ($type >= self::STRING) {
2.   $type -= self::STRING;
3.   if (is_string($value) && ($value == '')) {
4.     $this->_error(self::IS_EMPTY);
5.     return false;
6.   }
7. }

As you can probably see at this stage, ‘0‘ is both a string and not equal to ”, so it will pass the validation, and be counted as a valid response. It makes sense to a certain extent, but its a bit of a red herring when it comes to ensuring a checkbox is ticked.

The easiest solution we came up with was to use Zend_Validate_InArray to ensure the value we wanted was passed. This may seem like overkill if all we want to check for is ‘1‘, but if we have a series of checkboxes with different values, and one or more must be selected, this method will also work.

Source code

1. $objForm = new Zend_Form();
2.  
3. $objForm->setMethod('post');
4.  
5. $objCheck = $objForm->createElement('checkbox', 'test');
6.  
7. $objCheck->addValidator(new Zend_Validate_InArray(array(1)), false);
8.  
9. $objForm->addElement($objCheck);

This array can also be expanded if there are multiple values  that can be selected from, and one is required. As ‘0‘ is the default value set by the Zend Form Checkbox element, this will fail the validation if the checkbox isn’t checked.

I fully acknowledge this probably isn’t the most elegant method of accomplishing this task, so if you have any improvements or suggestions, please leave a comment!