Usar query personalizado en el modelo - Phalcon

empresa.php

<?php
use Phalcon\DI\FactoryDefault;

class Empresa extends \Phalcon\Mvc\Model
{
    public static function getall(){
      $query = "SELECT * from empresa";
      $db = self::getConnection();
      return $db->fetchAll($query, Phalcon\Db::FETCH_ASSOC);
    }

    public static function getConnection(){
        $di = FactoryDefault::getDefault();
        return $di->get('db');
    }

}