DBALExceptionResponseListener EventListener OnKernelResponse

DBALExceptionResponseListener.php

<?php
// src/AcmeBundle/EventListner/DBALExceptionResponseListener.php

namespace AcmeBundle\EventListener;

use Symfony\Component\HttpFoundation\RedirectResponse;
use Doctrine\DBAL\DBALException;
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
use Symfony\Component\HttpFoundation\Session\SessionInterface;
use Symfony\Component\HttpFoundation\Router\RouterInterface;

class DBALExceptionResponseListener
{
    public function __construct(SessionInterface $session, RouterInterface $router) 
    {
        $this->session = $session;
        $this->router  = $router;
    }

    /**
     * @param GetResponseForExceptionEvent $event
     */
    public function onKernelResponse(GetResponseForExceptionEvent $event)
    {
        $request = $event->getRequest();
        $exception =  $event->getException();
        $message = $exception->getMessage();

        // Maybe some checks on the route
        if ($request->get('_route') !== 'your_route' || $request->headers->get('referer') !== 'your_referer') {
            return;
        }

        // Listen only on the expected exception
        if (!$exception instanceof DBALException) {
            return;
        }

        // You can make some checks on the message to return a different response depending on the MySQL error given.
        if (strpos($message, 'Integrity constraint violation')) {
            // Add your user-friendly error message
            $this->session->getFlashBag()->add('error', 'SQL Error: '.$message);   
        }

        // Create your custom response to avoid the error page.
        $response = new RedirectResponse($this->router->generate('your_route'));

        // Update the Event Response with yours
        $event->setResponse($response);
    }
}

services.yml

# app/config/services.yml

services:
    acme.kernel.listener.dbal_exception_response_listener:
        class: AcmeBundle\EventListener\DBALExceptionResponseListener
        tags:
            - {name: kernel.event_listener, event: kernel.exception, method: onKernelResponse}
        arguments: 
            session: "@session"
            router: "@router"