FuelPHP Form Validation - Require field if another field is set and/or another field has a certain value.

gistfile1.php

<?php

/*

required_if Custom Validation Method

// Example 1 - require field if another field has been set
// Require the Billing State field if Billing Country has a value
$val = Validation::forge();
$val->add_callable('customvalidation');
$val->add_field('billing_country', 'Billing Country','required');
$val->add_field('billing_state', 'Billing State','required_if[billing_country]');

// Example 2 - require field if another field has a specific value
// Require the Billing State field if Billing Country equals "US"
$val = Validation::forge();
$val->add_callable('customvalidation');
$val->add_field('billing_country', 'Billing Country','required');
$val->add_field('billing_state', 'Billing State','required_if[billing_country,US]');

*/

class Customvalidation 
{
	public static function _validation_required_if($value,$check_field=null,$check_value=null)
	{
		// grab the active validation
		$validation = Validation::active();

		if (!empty($validation))
		{
			$validation->set_message('required_if', ':label is required.');
		
			// check_field is required
			if (empty($check_field))
			{
				return false;
			}
		
			// get the value of the check_field
			$field_value = $validation->validated($check_field);
		
			if (empty($check_value))
			{
				// if check_value is empty, return whether or not field_value has a value
				return !(!empty($field_value) && empty($value));
			}
			else
			{
				// else, check if field_value equals the check_value
				if (!empty($field_value) && $field_value==$check_value)
				{
					// if field_value exists and its value equals the check_value, return true if value is not empty
					return !empty($value);
				}
				else
				{
					// since field_value is empty OR the field_value and check_value don't match, the field in question is not required
					return true;
				}
			}
		}

		return false;
	}
}

?>