title: difference between get('doctrine'); and getDoctrine();
body: <p>In Symfony, I found three ways for accessing doctrine service and entity manager as follow:</p>
  
  <pre><code>$em = $this-&gt;getDoctrine()-&gt;getManager();
  
  $em = $this-&gt;get('doctrine')-&gt;getEntityManager();
  
  $em = $this-&gt;container-&gt;get('doctrine.orm.entity_manager');
  </code></pre>
  
  <p>Can anyone kindly explain their differences please and explain when should we use which of them.</p>