EntityAbstract.php

<?php

  namespace Entities;

  /**
   * @MappedSuperclass
   */
  abstract class EntityAbstract
  {

    /**
     * @Id
     * @Column(name="id", type="smallint")
     * @GeneratedValue(strategy="AUTO")
     */
    private $_id;

    final public function getId ()
    {
      if ( ! $this->hasId())
      {
        throw new \OutOfBoundsException(sprintf('No id was set for this %s instance', get_class($this)));
      }

      return $this->_id;
    }

    final public function setId ($arg_id)
    {
      if ($this->hasId())
      {
        throw new \BadMethodCallException(sprintf('The %s#setId method can not be called when an id is already set', get_class($this)));
      }

      $this->_id = $arg_id;
    }

    final public function hasId ()
    {
      return NULL !== $this->_id;
    }

    final public function voidId ()
    {
      if ( ! $this->hasId())
      {
        throw new \BadMethodCallException('Cannot void the id for this %s intance since no id is set');
      }

      $this->_id = NULL;
    }

    public function __get ($arg_key)
    {
      $method = 'get' . ucfirst($arg_key);

      if ( ! method_exists($this, $method))
      {
        throw new \OutOfBoundsException(sprintf('The %s object does not have a field getter named %s.', get_class($this), $method));
      }

      return call_user_func(array($this, $method));
    }

    public function __set ($arg_key, $arg_value)
    {
      $method = 'set' . ucfirst($arg_key);

      if ( ! method_exists($this, $method))
      {
        throw new \OutOfBoundsException(sprintf('The %s object does not have a field setter named %s.', get_class($this), $method));
      }

      return call_user_func(array($this, $method), $arg_value);
    }

  }

Fan.php

<?php

  namespace Entities;

  /**
   * @Entity
   * @Table(name="users")
   * @InheritanceType("SINGLE_TABLE")
   * @DiscriminatorColumn(name="type", type="string")
   * @DiscriminatorMap({"idol" = "Entities\Idol", "fan" = "Entities\Fan"})
   */
  class Fan extends EntityAbstract
  {

//  /**
//   * @ManyToMany(targetEntity="Entities\Idol", mappedBy="_idols")
//   */
//  private $_idols;

    public function __construct ()
    {
      parent::__construct();
//    $this->_idols = new \Doctrine\Common\Collections\ArrayCollection();
    }

  }

Idol.php

<?php

  namespace Entities;

  /**
   * @Entity
   */
  class Idol extends Fan
  {

    /**
     * @ManyToMany(targetEntity="Entities\Fan")
     * @JoinTable(name="idol_fans"
     *           ,joinColumns={@JoinColumn(name="idol_id", referencedColumnName="id")}
     *           ,inverseJoinColumns={@JoinColumn(name="fan_id", referencedColumnName="id")}
     *           )
     */
    private $_fans;

    public function __construct ()
    {
      parent::__construct();

      $this->_fans = new \Doctrine\Common\Collections\ArrayCollection();
    }

    public function getFans ()
    {
      return $this->_fans;
    }

    public function setFans (array $arg_fans)
    {
      $this->_fans = new \Doctrine\Common\Collections\ArrayCollection(array_filter($arg_fans, array($this, '_filterFan')));
    }

    private function _filterFan (UserHyvesXfactorFan $arg_fan)
    {
      return true;
    }

  }