从DB symfony 4开始获取最大值形式

// src/Entity/Product.php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity(repositoryClass="App\Repository\ProductRepository")
 */
class Product
{
    // ...

    /**
     * @ORM\Column(type="decimal", precision=10, scale=2)
     */
    private $price;

    // ...

    /**
     * 获取最大价格
     */
    public function getMaxPrice()
    {
        $qb = $this->createQueryBuilder('p');
        $qb->select('MAX(p.price) as max_price');

        $result = $qb->getQuery()->getSingleScalarResult();

        return $result;
    }

    // ...
}

// src/Controller/ProductController.php

namespace App\Controller;

use App\Entity\Product;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Routing\Annotation\Route;

class ProductController extends AbstractController
{
    /**
     * @Route("/product/max-price", name="product_max_price")
     */
    public function getMaxPrice()
    {
        $productRepository = $this->getDoctrine()->getRepository(Product::class);
        $maxPrice = $productRepository->getMaxPrice();

        return $this->render('product/max_price.html.twig', [
            'maxPrice' => $maxPrice,
        ]);
    }
}