title: Symfony2 - Set default value in entity constructor
body: <p>I can set a simple default value such as a string or boolean, but I can't find how to set the defualt for an entity.</p>
  
  <p>In my User.php Entity:</p>
  
  <pre><code>/**
  * @ORM\ManyToOne(targetEntity="Acme\DemoBundle\Entity\Foo")
  */
  protected $foo;
  </code></pre>
  
  <p>In the constructor I need to set a default for $foo:</p>
  
  <pre><code>public function __construct()
  {
      parent::__construct();
  
      $this-&gt;foo = 1; // set id to 1
  }
  </code></pre>
  
  <p>A Foo object is expected and this passes an integer.</p>
  
  <p>What is the proper way to set a default entity id?</p>