<?php
namespace App\Entity;

/**
 * @ORM\Table(name="a")
 * @ORM\Entity
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="type", type="string")
 * @ORM\DiscriminatorMap({
 *     "B",
 *     "my_c_type" = "C",
 * })
 */
abstract class A
{
   /**
     * @var string
     *
     * @ORM\Column(name="some_attribute_from_a", type="string", length=255, nullable=false)
     */
    public $someAttributeFromA;
}