Custom find methods

gistfile1.php

<?php
class Page extends AppModel {

    var $_findMethods   = array(
        'index'         => true,
    );

    function _findRevision($state, $query, $results = array()) {
        if ($state == 'before') {
            if (empty($query['slug'])) {
                throw new InvalidArgumentException(__('Invalid page', true));
            }
            if (empty($query['rev_id'])) {
                throw new InvalidArgumentException(__('Invalid revision', true));
            }
            $query['conditions'] = array("Page.slug" => $query['slug']);
            $query['fields'] = array(
                'Page.id', 'Page.title', 'Page.slug',
                'Revision.id', 'Revision.version_id', 'Revision.edit_summary', 'Revision.content',
                'Revision.version_created',
            );
            $query['joins'] = array(array(
                'table' => 'pages_revs',
                'alias' => 'Revision',
                'type' => 'INNER',
                'foreignKey' => false,
                'conditions'=> array(
                    "Revision.version_id = {$query['revision']}",
                    'Revision.id = Page.id'
                ),
                'limit' => '1',
            ));
            $query['limit'] = 1;
            unset($query['slug']);
            unset($query['revision']);
            return $query;
        } elseif ($state == 'after') {
            if (empty($results[0])) {
                throw new OutOfBoundsException(__('Invalid page', true));
            }
            return $results[0];
        }
    }
}

class PagesController extends AppController {
    function revision($rev_id = null, $title = null) {
        try {
            $page = $this->Page->find('revision', array(
                'slug' => $title,
                'revision' => $rev_id,
            ));
        } catch (Exception $e) {
            $this->redirect(array('action' => 'index'));
        }

    }
}