public function calculateChangeSet()
    {
        $set = [];
        foreach ($this->current as $key => $current) {
            $original = isset($this->original[$key]) ? $this->original[$key] : null;
            $set[$key]['old'] = $original;
            $set[$key]['new'] = $current;
        }
        foreach ($this->remove as $key) {
            $set[$key]['old'] = $this->original[$key];
            $set[$key]['new'] = null;
        }
        ksort($set);
        return $set;
    }