li3 Validation Example Using Multiple Form Inputs

validator.php

/**
 * Example: Sometimes you need a bit more validation power on form inputs. For instance, a form validation
 * may be dependpent on multiple inputs and advanced testing.
 *
 * The example below shows the power of $options array. That's where all your form inputs along with some other custom
 * parts will be stored. The key to getting access to your form POST data is through `values` which lives in $options.
 * The extract method pulls out the 'values' array providing access to the POST data.
 *
 * In this particular example were trying to check if the field input `acronym` is unique among a list of cities in MongoDB.
 *
 */
Validator::add('isUniqueAcronym', function($value, $format = null, array $options = array()) {
    $options += array(
        'values' => array()
    );
    extract($options);
    $conditions['acronym'] = $value;
    $conditions['cities'] = ['$in' => $values['cities']];
	$stuff = Stuff::count(compact('conditions'));
	return ($stuff == 0) ? true : false;
});
?>

A side note: If your input has nested data (i.e. a multi-select dropdown) then your array keys will be in dot notation. Make use of the expand method in\lithium\util\Set to turn your dot-notation into a multi-dimensional array.