Programmatically: How to use Magento's custom validation mechanism for custom form validation

Step 1: Create a custom validation class

Create a new PHP file, e.g., MyCompany/MyModule/Model/Form/Validator/MyValidation.php:

	class MyCompany_MyModule_Model_Form_Validator_MyValidation
    extends Mage_Core_Model_Form_Validator_Abstract
  {
    public function validate($object)
    {
        // Your custom validation logic goes here
        // For example, let's say we want to validate a password field
        $password = $object->getData('password');
        if (strlen($password) < 8) {
            $this->_addError('Password must be at least 8 characters');
        }
        return $this->_getMessages();
    }
 }
	

Step 2: Register the validation class in your module's config file

Add the following code to your module's etc/config.xml file:

		
	
    
    
        
            
                MyCompany_MyModule_Model
            
        
        
            
                MyCompany_MyModule_Model_Form_Validator_MyValidation
            
        
    
    
	
	

Step 3: Use the custom validation class in your form

Modify your form's XML file (e.g., app/design/frontend/yourtheme/template/form.phtml) to include the custom validation class:

Step 4: Test your custom validation

Submit your form with a password that is too short (e.g., less than 8 characters). You should see an error message indicating that the password is too short.