title: difference between 'detach' and 'remove' entityManager's methods
body: <p>I would like to know what's the real difference between <code>em.detach(entity)</code>, <code>em.remove(entity)</code> and using a <code>JPQL</code> request like :</p>
  
  <pre><code>em.createQuery("DELETE FROM Country").exceuteUpdate();
  </code></pre>
  
  <p>thanks.</p>