Abstract Class for Doctrine entity - symfony

Question

I am trying to make an abstract class for my entities involving general fields like created_at and updated_at values:
<?php
namespace AppBundle;
use Doctrine\ORM;
abstract class Model {
/**
* #var \DateTime $created_at
*
* #ORM\Column(type="datetime")
*/
private $created_at;
/**
* #var \DateTime $updated_at
*
* #ORM\Column(type="datetime")
*/
private $updated_at;
}
Then, I extend my class:
<?php
namespace AppBundle\Entity;
use AppBundle\Model;
/**
* Entity
*
* #ORM\Table()
* #ORM\Entity(repositoryClass="RB\ProductsBundle\Entity\ProductRepository")
*/
class Entity extends Model
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=255, nullable=true)
*/
private $name;
}
The problem is: When I make a php app/console doctrine:schema:update --dump-sql, it doesn't recognize the Model fields. How can I change that? Should I use a trait or something like that?
EDIT: I tried to add * #ORM\MappedSuperclass at the top of my abstract class with no luck

Answer 1

The problem is likely to be that your properties in the abstract parent class are defined as private. Change them to protected and it should work.
As an aside, I use traits for this purpose, rather than inheritance, as your entity classes can use multiple traits, but they can only extend one abstract class.