<?php

/**
 * @Entity
 * @Traits({"B", "C"})
 */
class A
{
  /** @Id @Column(type="integer") @GeneratedValue */
  public $id;
}

/** @Trait */
abstract class B
{
  /** @Column(type="string") */
  public $traitProperty1;
}

/** @Trait */
abstract class C
{
  /** @Column(type="string") */
  public $traitProperty12;
}

// Then when you run code generation you end up with something like this:

/**
 * @Entity
 * @Traits({"B", "C"})
 */
class A extends BaseA
{
  /** @Id @Column(type="integer") @GeneratedValue */
  public $id;

  /** @Column(type="string") */
  public $traitProperty1;

  /** @Column(type="string") */
  public $traitProperty12;
}

class BaseA
{
  public $id;

  public $traitProperty1;

  public $traitProperty12;
}