Selective mapping inheritance in Doctrine2

BaseEntity.php

<?php

namespace App\Util\Doctrine\Entity;

/**
 * Base Entity.
 */
class BaseEntity
{
    /**
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="IDENTITY")
     */
    protected $id;
    
    /** @ORMColumn(type="string") */
    protected $foo;
}

CanHaveExtraFieldsTrait.php

<?php

namespace App\Util\Doctrine\Entity;

use App\Util\Doctrine\Entity\BaseEntity as Base;

trait CanHaveExtraFieldsTrait extends Base
{
    /** @ORM\Column(type="string") */
    protected $bar;
}

ChildWithExtraFields.php

<?php

namespace App\AcmeBundle\Entity;

use App\Util\Doctrine\Entity\BaseEntity as Base;
use App\Util\Doctrine\Entity\CanHaveExtraFieldsTrait as ExtraFields;

/**
 * @ORM\Entity
 * @ORM\Table(name="childs")
 */
class ChildWithExtraFields extends Base
{
    use ExtraFields;
    
    // Properties: id, foo, bar 
}

ChildWithoutExtraFields.php

<?php

namespace App\AcmeBundle\Entity;

use App\Util\Doctrine\Entity\BaseEntity as Base;

/**
 * @ORM\Entity
 * @ORM\Table(name="childs")
 */
class ChildWithExtraFields extends Base
{
    // Properties: id, foo 
}