private function getJsonInstance($property)
    {
        if(!$this->isJsonProperty($property))
            throw new JsonPropertyException("Requested property '{$property}' is not a valid for '".get_class($this->model)."'.");

        if(!array_key_exists($property, $this->jsonInstances))
            $this->jsonInstances[$property] = new JsonProperty( $this->model, $property );

        return $this->jsonInstances[$property];
    }