Doctrine ORM：如何在映射表中添加记录？

I have two Entities: Role and Right. There's a many to many relationship between them. The joining table role_rights has no entity defined. It has two fields: role_id and right_id. So I have done following:

Role Entity

class Role
{
  /**
     * Many Roles have Many Rights.
     * @ORM\ManyToMany(targetEntity="Right")
     * @ORM\JoinTable(name="role_has_right",
     *      joinColumns={@ORM\JoinColumn(name="role_id", referencedColumnName="id")},
     *      inverseJoinColumns={@ORM\JoinColumn(name="right_id", referencedColumnName="id")}
     *      )
     */
    private $rights;

 public function __construct()
    {
        $this->rights = new ArrayCollection();
        $this->creationDate = new \DateTime("now");
        $this->updateDate = new \DateTime("now");
        $this->deleteDate = null;
    }

  /**
 * @param Right $right
 */
  public function addRight($right)
  {
    $this->rights[] = $right;
  }
}

Role Data Access

class RoleDAO extends EntityRepository {
public function assignRoles($role_id,$right_id) {

        $role_info = $this->find($role_id);
        $right_info = $this->find($right_id);
        $role_info->addRight($right_info);
        $em = $this->getEntityManager();
        $em->persist($role_info);
        $em->flush();
 }
}

And it's giving error:

Expected value of type "Doctrine\Common\Collections\Collection|array" for association field "App\Model\Entities\Role#$rights", got "App\Model\Entities\Role" instead.

Goal is to add role and relative rights'IDs in mapped table.

Thanks