public function getOrCreate($className, $params = array())
    {
        $key = $className . join('-', $params);

        if (isset($this->mapping[$key])) {
            return $this->mapping[$key];
        }

        if (method_exists($this, $this->getMethodName($className))) {
            $callback = array($this, $this->getMethodName($className));
            $instance =  call_user_func_array($callback, $params);
        } else {
            $instance = new $className;
        }

        return $this->mapping[$key] = $instance;
    }