public function createVariantAttributeRelation($productId, array $requestData)
    {
        $variant = $this->retrieveProductById($productId);
        $attribute = $this->retrieveAttributeById($this->getProperty($requestData, 'attributeId'));

        // Only add if relation does not already exists.
        if (!$variant->getVariantAttributes()->contains($attribute)) {
            $variant->addVariantAttribute($attribute);
        }

        return $variant;
    }