/*
 * CakePHP: Add a custom function to model field validation.
 * In this case it makes sure that an email address can occur multiple times,
 * but it can only occur with another where column 'site_name' equals $foo
 * once
 */
var $validate = array(
		'email' => array(
		    'form' => array(
                    'rule' => 'email',
                    'message' => 'Please enter a valid email address',
                    'allowEmpty' => false,
		    'last' => true
	        ),
		    'unique' => array(
	            'rule' => array('checkUnique'),
	            'message' => 'You are already registered',
	            'allowEmpty' => false,
		    'last' => true,
                    'on' => 'create' // only use this rule on field creation, not update
	        )
	)
);

function checkUnique($arrEmail) {
		$intCount = $this->find('count', array(
			'conditions' => array(
			'site_name' => $foo,
			'email' => $arrEmail['email']
		)));

		return $intCount == 0 ? true : false;
	}