title: How extends User entity of FOSUserBundle?
body: <p>I have my UserBundle who extends the FOSUserBundle and works fine. But now, I want create multiple users entities with différents properties.
  But the problem is when I create my user enttity who extends my main User entity like this :</p>
  
  <pre><code>class User extends BaseUser
  {
      protected $id;
      // The main user class who extends FOSUser entity
  }
  
  class UserB extends User
  {
      //
  }
  </code></pre>
  
  <p>When I do this, I've got an error : `</p>
  
  <blockquote>
    <p>Access level to MyApp\UserBundle\Entity\UserB::$id must be protected (as in class MyApp\UserBundle\Entity\User).</p>
  </blockquote>
  
  <p>And when I create a protected id in my UserB entity I have this: </p>
  
  <blockquote>
    <p>PHP Fatal error:  Cannot redeclare MyApp\UserBundle\Entity\UserB::$id.</p>
  </blockquote>
  
  <p>And to finish, I can't delete the id in my User entity less return a Doctrine error :</p>
  
  <blockquote>
    <p>[Doctrine\ORM\Mapping\MappingException]<br>
        No identifier/primary key specified for Entity 'MTS\UserBundle\Entity\User'. Every           Entity must have an identifier/primary key.</p>
  </blockquote>
  
  <p>Someone can help me ?</p>
  
  <p>EDIT : Problem solved. My code :</p>
  
  <pre><code>/**
   * MTS\UserBundle\Entity\User
   *
   * @ORM\Entity
   * @ORM\InheritanceType("SINGLE_TABLE")
   * @ORM\DiscriminatorColumn(name="type", type="string")
   * @ORM\DiscriminatorMap({"userfb" = "UserFB"})
   */
  abstract class User extends BaseUser
  {
      /**
       * @var integer $id
       *
       * @ORM\Column(name="id", type="integer")
       * @ORM\Id
       * @ORM\GeneratedValue(strategy="AUTO")
       */
      protected $id;
  
      /**
       * @var string $type
       */
      private $type;
  }
  
  /**
   * @ORM\Table()
   * @ORM\Entity()
   */
  class UserB extends User
  {
      // My variables
  }
  </code></pre>