Symfony/Doctrine ORM mapping not detected - php

Question

I'm building my first Symfony bundle. I want to use Models instead of Entity so I have a directory Model which contains only one model. Also I have a mapping for this model which is located in Resources/config/doctrine/mymodel.orm.yaml. When I run /bin/console doctrine:migration:diff it says No changes detected in your mapping information
Here's is my model
class MyModel
{
/**
* #var mixed
*/
private $id;
/**
* #var string
*/
private $user;
/**
* #return mixed
*/
public function getId()
{
return $this->id;
}
/**
* #return null|string
*/
public function getUser(): ?string
{
return $this->user;
}
/**
* #param string $user
*
*/
public function setUser(string $user): self
{
$this->user = $user;
return $this;
}
and the mymodel.orm.yaml
MyNamespace\MyBundle\Model\MyModel:
type: mappedSuperclass
repositoryClass: MyNamespace\MyBundle\Repository\MyModelRepository
id:
id:
type: integer
generator:
strategy: AUTO
fields:
user:
type: string
What I'm missing here?
UPDATE
I'm using symfony 4.2.3
Here's my doctrine.yaml
parameters:
env(DATABASE_URL): ''
doctrine:
dbal:
driver:
charset: utf8
default_table_options:
charset: utf8
collate: utf8_unicode_ci
url: '%env(resolve:DATABASE_URL)%'
orm:
auto_generate_proxy_classes: '%kernel.debug%'
entity_managers:
default:
auto_mapping: true
mappings:
MyBundle: ~