title: Best way for extending a entity in doctrine
body: <p>I have a User Entity in a small Framework made by me. Now i want to use this User Entity in several projects.
  But in some projects I want to add a few fields to the User Entity without modifying the file.</p>
  
  <p>What I tried so far:</p>
  
  <p>I created a new DefaultUser Entity in a DefaultUser Bundle and made the User Entity a mappedsuperclass. But now I can't make a association in other entities like</p>
  
  <pre><code>    /*
       * @ORM\ManyToOne(targetEntity="User", inversedBy="jobs")
       * @ORM\JoinColumn(name="user", referencedColumnName="id")
       */
       private $user;
  </code></pre>
  
  <p>Because Doctrine can't find the id column in the user entity. This only works if I specify the DefaultUser Entity. According to the doctrine documentation this only works on many to many associations if only one leaf exists. </p>
  
  <p>Then I tried Single Table Inheritance. This works fine but I have to modify the DiscriminatorMap if I want to extend my user entity which is shared acros multiple projects...</p>
  
  <p>So whats the best way to extend the UserEntity?</p>