如何解决Symfony 4中的KnpPaginator异常（即使应用容器中存在服务”knp_paginator”，也找不到）

此异常出现在使用早期版本(Symfony 3)中的代码的Symfony 4项目中, 其中通过服务容器请求服务, 例如, 以下控制器应引发异常：

< ?phpnamespace App\Controller; use Symfony\Bundle\FrameworkBundle\Controller\Controller; use Symfony\Component\HttpFoundation\Request; use Symfony\Component\HttpFoundation\Response; use ReCaptcha\ReCaptcha; use Doctrine\ORM\Query\Expr\Join; use App\Entity\FosUser; // Note as well that extends the 'Symfony\Bundle\FrameworkBundle\Controller\Controller' class // which is deprecated in Symfony 4class AuthorsController extends Controller{// Controller that shows all the news from x repositorypublic function show(Request $request, FosUser $user){$em = $this-> getDoctrine()-> getManager(); $repoArticles = $em-> getRepository('App:News'); $pagination = $repoArticles-> createQueryBuilder('a')-> where('a.published = 1')-> andWhere('a.author = :user')-> orderBy('a.datepublished', 'DESC')-> setParameter('user', $user-> getId())-> getQuery()-> getResult(); // Important: and paginates the query with knp paginator, however accesing the service container$paginator = $this-> get('knp_paginator'); $entities = $paginator-> paginate($pagination, $request-> query-> getInt('page', 1), 14); return $this-> render('news/show.html.twig', array('user' => $user, 'entities' => $entities)); }}

代码中描述的问题是由你尝试访问KNP的分页器服务引起的。在本文中, 我们将向你简要介绍如何在Symfony 4项目中解决此异常。
解基本上, 解决此问题所需要做的是分析现有代码, 并从何处请求分页器服务。如果从服务容器中需要它, 则需要删除该变量, 并将PaginatorInterface直接注入控制器。这将公开与在服务容器中工作方式相同的变量, 还要注意, 控制器需要扩展AbstractController类, 而不是Controller类, 因为这将防止将来的弃用警告：

< ?phpnamespace App\Controller; // 1. Include the AbstractController classuse Symfony\Bundle\FrameworkBundle\Controller\AbstractController; // 2. The controller extends now the AbstractControllerclass ExampleController extends AbstractController{// 3. The paginator is injected in the action $paginatorpublic function exampleaction(PaginatorInterface $paginator){$em= $this-> get('doctrine.orm.entity_manager'); $dql= "SELECT a FROM AcmeMainBundle:Article a"; $query = $em-> createQuery($dql); // 3. Use paginator to do something with the paginator$pagination = $paginator-> paginate($query, /* query NOT result */$request-> query-> getInt('page', 1), /*page number*/10 /*limit per page*/); }}

我们的例子的解决方案
以下代码段显示了如何通过AbstractController的实现正确修复初始示例, 以及如何将分页器直接插入动作中：

< ?phpnamespace App\Controller; // Use the abstract controller insteaduse Symfony\Bundle\FrameworkBundle\Controller\AbstractController; use Symfony\Component\HttpFoundation\Request; use Symfony\Component\HttpFoundation\Response; use ReCaptcha\ReCaptcha; use Doctrine\ORM\Query\Expr\Join; use App\Entity\FosUser; // The controller extends now the AbstractControllerclass AuthorsController extends AbstractController{// Controller that shows all the news from x repository// The paginator is injected in the action $paginatorpublic function show(Request $request, FosUser $user, PaginatorInterface $paginator){$em = $this-> getDoctrine()-> getManager(); $repoArticles = $em-> getRepository('App:News'); $pagination = $repoArticles-> createQueryBuilder('a')-> where('a.published = 1')-> andWhere('a.author = :user')-> orderBy('a.datepublished', 'DESC')-> setParameter('user', $user-> getId())-> getQuery()-> getResult(); $entities = $paginator-> paginate($pagination, $request-> query-> getInt('page', 1), 14); return $this-> render('news/show.html.twig', array('user' => $user, 'entities' => $entities)); }}

【如何解决Symfony 4中的KnpPaginator异常（即使应用容器中存在服务” knp_paginator” ，也找不到）】编码愉快！