title: Django QuerySet Filter by week_day returning nothing
body: <p>I am currently trying to filter my QuerySet results by the day of the week in Django 2.0.<br>
  I can't for the life of me get the django <a href="https://docs.djangoproject.com/en/2.0/ref/models/querysets/#week-day" rel="nofollow noreferrer">week_day</a> filter <code>datetime__week_day</code> to return any results.</p>
  
  <p><strong>Model</strong></p>
  
  <pre><code>class Session(models.Model):
      def __str__(self):
          return str.join(', ', (str(self.game.name), str(self.datetime_created), str(self.start)))
  
      game = models.ForeignKey(
          'Game',
          on_delete=models.PROTECT,
          blank=False,
          null=False,
      )
  
      datetime_created = models.DateTimeField(auto_now_add=True,)
      start = models.DateTimeField(blank=True, null=True,)
      end_time = models.TimeField(blank=True, null=True,)
      competitive = models.BooleanField(default=False,)
  </code></pre>
  
  <p><strong>Filtering</strong></p>
  
  <pre><code>filtered_sessions = Session.objects.filter(
      start__week_day=2,
  ).exclude(start__isnull=True)
  </code></pre>
  
  <p>I currently have an entry in the sessions table (MySQL backend) which contains the datetime <code>2018-04-30 23:51:42.000000</code>, so I would expect this QuerySet to contain that 'Session' as it occurs on a Monday.  </p>
  
  <p>Referring back to the documentation, The week goes from Sunday(1) to Saturday(7).<br>
  I have <code>USE_TZ</code> in my settings, <code>TIME_ZONE='UTC'</code>.<br>
  Irrespective of these settings, I have also tried replacing the <code>start__week_day=2</code> with values from 0-8 (inclusive, just in case)  </p>
  
  <p>My question is this: Why is what I am trying is not returning any results?  </p>
  
  <p>Please let me know if I've left out something that would help answer my query.<br>
  Thanks!</p>
  
  <p><strong>EDIT:</strong>
  I have since attempted to run a direct query in the database (<code>SELECT * FROM mysite_session WHERE DAYOFWEEK('start') IN (0-8);</code>)<br>
  No result in the database.</p>