Zend_Validate_Callback Success on False

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What if you need to validate input using a callback function that will return False when the input is valid? Here's a custom validator to do the job.

class My_Validate_Callback_False extends Zend_Validate_Callback
    public function isValid($value, $context = NULL)
        // Run the validator normally and collect the result.
        $result = parent::isValid($value, $context);

        if($result) {
            // The callback returned TRUE, so we should return FALSE.
            return FALSE;
        } elseif(in_array(self::INVALID_CALLBACK, $this->_errors)) {
            // The callback errored.  We should persist the FALSE result.
            return FALSE;
        } else {
            // The callback returned FALSE and did not error.  Clear the errors and return TRUE.
            $this->_errors = array();
            return TRUE;

When would you use this?

If you wrote the callback function, you control the result. But if your callback function is built into PHP or a library, it may not be so easy. You could wrap the function with a version that reverses the result, or you can use My_Validate_Callback_False.

For example, I have a user registration form with a CAPTCHA. New usernames are checked in the database for uniqueness. But I don't want to query the database unless the user has passed the CAPTCHA — this combats automated queries that probe for usernames. So the username validation chain includes a callback to Zend_Form_Element_Captcha->hasErrors().

$username = new Zend_Form_Element_Text('username');
$username->addPrefixPath('My_Validate', 'My/Validate/', 'validate')
         ->addValidator('Callback_False', TRUE, array(
               'callback' => array($captcha, 'hasErrors')));

Because hasErrors() will return False when the input is valid, I need My_Validate_Callback_False to reverse the normal behavior.



Hi! I'm Drew, the Wimpy Programmer. I'm a software developer and formerly a Windows server administrator. I use this blog to share my mistakes and ideas.