private function setOrderByFieldIndices()
    {
        $keyParts = $this->explodeKey($this->key);

        foreach ($this->orderBys as $field => $order) {
            $needle = $this->fieldWrapper[0] . $field . $this->fieldWrapper[1];
            $this->orderByFieldIndices[array_search($needle, $keyParts)] = $order;
        }
    }