title: Django count grouping by year/month without extra
body: <p>I'm working with django 1.9</p>
  
  <p>Model : </p>
  
  <pre><code>class Comment(models.Model):
      title = models.CharField(max_length=250, null=False)
      date = models.DateField(auto_now_add=True)
  </code></pre>
  
  <p>As 'extra()' will be deprecated in django i try to figure out how to count Comments group by year-month without using 'extra'</p>
  
  <p>Here is the code with extra : </p>
  
  <pre><code>Comment.objects.extra(select={'year': "EXTRACT(year FROM date)",
      'month': "EXTRACT(month from date)"})\
      .values('year', 'month').annotate(Count('pk'))
  </code></pre>
  
  <p>Thank you for your help.</p>