Sonata\ProductBundle\Entity\ProductManager::updateStock PHP Method

    public function updateStock($product, $diff)
    {
        if (0 == $diff) {
            return;
        }
        $productId = $product instanceof ProductInterface ? $product->getId() : $product;
        $tableName = $this->getTableName();
        $operator = $diff > 0 ? '+' : '-';
        $this->getConnection()->query(sprintf('UPDATE %s SET stock = stock %s %d WHERE id = %d;', $tableName, $operator, abs($diff), $productId));
    }