title: Doctrine and composite unique keys
body: <p>I want to do composite unique key in doctrine.
  Those are my fields:</p>
  <pre class="lang-php prettyprint-override"><code>/**
   * @var string $videoDimension
   *
   * @Column(name=&quot;video_dimension&quot;, type=&quot;string&quot;, nullable=false)
   */
  private $videoDimension;
  
  /**
   * @var string $videoBitrate
   *
   * @Column(name=&quot;video_bitrate&quot;, type=&quot;string&quot;, nullable=false)
   */
  private $videoBitrate;
  </code></pre>
  <p>How can I show doctrine, that those combined together are composite unique key?</p>