title: Unique Id for all the entities from all repositories
body: <p>In PHPCR (NoSQL) there is something like Uuid (it's something different than Id in the table, unique only for the single table) - the Id that is unique to all Documents (Entities) in the whole data base. It's of much help when e.g. using forms, because I can use Uuid without knowing the exact class of an entity, and still being able to access directly a related record just by:</p>
  
  <pre><code>$objectManager-&gt;find(null, $uuid);
  </code></pre>
  
  <p>I'd like to have a similar solution with the RDBMS in the Doctrine ORM, i.e. to find a record when knowing only its unique id (Uuid). Do anyone of you know about such a solution?</p>
  
  <p><strong>From the PHPCR-ODM documentation:</strong></p>
  
  <p><a href="http://docs.doctrine-project.org/projects/doctrine-phpcr-odm/en/latest/reference/basic-mapping.html#doctrine-mapping-types" rel="nofollow noreferrer">http://docs.doctrine-project.org/projects/doctrine-phpcr-odm/en/latest/reference/basic-mapping.html#doctrine-mapping-types</a></p>
  
  <blockquote>
    <p>Each document can have a unique identifier for referencing it. While the uuid is also exposed as a read-only string property, the proper mapping for it is mapping it as UUID.</p>
  </blockquote>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>Here are the Doctrine's sources:</p>
  
  <p>From the general Doctrine common lib <a href="https://github.com/doctrine/common/blob/master/lib/Doctrine/Common/Persistence/ObjectManager.php#L42" rel="nofollow noreferrer">https://github.com/doctrine/common/blob/master/lib/Doctrine/Common/Persistence/ObjectManager.php#L42</a></p>
  
  <pre><code>public function find($className, $id);
  </code></pre>
  
  <p>From the ORM <a href="https://github.com/doctrine/doctrine2/blob/master/lib/Doctrine/ORM/EntityManager.php#L380" rel="nofollow noreferrer">https://github.com/doctrine/doctrine2/blob/master/lib/Doctrine/ORM/EntityManager.php#L380</a></p>
  
  <pre><code>public function find($entityName, $id, $lockMode = null, $lockVersion = null)
  </code></pre>
  
  <p>But I don't stick to find() method.</p>