Yii model input validation. Checking that at least one of a given set of attributes is set.

needOneOf.php

<?php

public function rules() {
    return array(
        array('a', 'needOneOf', 'or' => array('b', 'c', 'd')),
    );
}

public function needOneOf($attr, $params) {
    array_unshift($params['or'], $attr);
    foreach ($params['or'] as $attr) {
        if ($this->$attr !== null) {
            return;
        }
    }
    $this->addError('summary', Yii::t('app',
        'At least one of {attrs} must be set.',
        array('{attrs}' => implode('|', $params['or']))
    ));
}