title: Doctrine 2 One-To-One unidirectional relationship delete non-owning side
body: <p>I have two entities with a one-to-one unidirectional relationship:</p>
  
  <pre><code>class Foo {
   ...
  /**
   * @OneToOne(targetEntity="Bar")
   */
  private $bar;
  ...
  }
  
  class Bar {
  ...
  }
  </code></pre>
  
  <p>When I try to delete a Bar entity I get this error:</p>
  
  <blockquote>
    <p>Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails </p>
  </blockquote>
  
  <p>How do I keep a unidirectional relationship without loosing the ability to delete Bar entities?</p>