namespace AppBundleRepository;
use DoctrineORMEntityRepository;
class UserRepository extends EntityRepository
{
    public function findByRole($role)
    {
        $qb = $this->_em->createQueryBuilder();
        $qb->select('u')
            ->from($this->_entityName, 'u')
            ->where('u.roles LIKE :roles')
            ->setParameter('roles', '%"'.$role.'"%');

        return $qb->getQuery()->getResult();
    }
}

WHERE
  p0_.roles::text LIKE '%ROLE_EMPLOYER%'

// Example - $qb->expr()->like('u.firstname', $qb->expr()->literal('Gui%'))
public function like($x, $y); // Returns ExprComparison instance

public function findByRole($role) {
    $qb = $this->getEntityManager()->createQueryBuilder();
    $qb->select('u')
            ->from($this->getEntityName(), 'u')
            ->where("u.roles LIKE '%$role%'")
    ;

    return $qb->getQuery()->getResult();
}

$qb = $this->_em->createQueryBuilder();
$qb->select('u')
    ->from($this->_entityName, 'u')
    ->where('u.roles LIKE :roles')
    ->setParameter('roles', ''%'.$role.'%'');

return $qb->getQuery()->getResult();

$ composer require "boldtrn/jsonb-bundle

doctrine:
    dbal:
        types:
          jsonb: BoldtrnJsonbBundleTypesJsonbArrayType
        mapping_types:
          jsonb: jsonb
    orm:
        dql:
            string_functions:
                JSONB_AG:   BoldtrnJsonbBundleQueryJsonbAtGreater
                JSONB_HGG:  BoldtrnJsonbBundleQueryJsonbHashGreaterGreater
                JSONB_EX:   BoldtrnJsonbBundleQueryJsonbExistence

$query = $this->getEntityManager()->createQuery("SELECT u FROM AppBundle:User u WHERE JSONB_HGG(u.roles , '{}') LIKE '%EMPLOYER%' ");
$users = $query->getResult();
return $users;