如何在symfony中显示数组关系ManyToMany

/**
 * @ORM\ManyToMany(targetEntity="App\Entity\Role")
 * @ORM\JoinTable(name="user_roles",
 *      joinColumns={@ORM\JoinColumn(name="user_id", referencedColumnName="id")},
 *      inverseJoinColumns={@ORM\JoinColumn(name="role_id", referencedColumnName="id")}
 * )
 */
private $roles;

/**
 * @ORM\ManyToMany(targetEntity="App\Entity\User", mappedBy="roles")
 */
private $users;

php bin/console doctrine:migrations:diff
php bin/console doctrine:migrations:migrate

public function showUserRoles(User $user)
{
    $roles = $user->getRoles();

    return $this->render('user_roles.html.twig', [
        'user' => $user,
        'roles' => $roles,
    ]);
}

<h1>User Roles</h1>

<p>User: {{ user.username }}</p>

<ul>
    {% for role in roles %}
        <li>{{ role.name }}</li>
    {% endfor %}
</ul>