public function getBySlug(Model $model, $slug) {
        return $model->find('first', array(
            'conditions' => array($model->alias . '.slug' => $slug),
            'contain' => array_keys($model->belongsTo),
            'cache' => array($model->alias . '::getBySlug', $slug),
            'cacheExpires' => $this->getExpiration($model)
        ));
    }