CartRepository.php

<?php

namespace Sylius\Bundle\CartBundle\Entity;

use Sylius\Bundle\ResourceBundle\Doctrine\ORM\EntityRepository;

class CartRepository extends EntityRepository
{
    protected function getQueryBuilder()
    {
        return parent::getQueryBuilder()
            ->select('cart, item')
            ->leftJoin('cart.items', 'item')
        ;
    }

    protected function getAlias()
    {
        return 'cart';
    }
}