title: Django: Group by date over a datetime field
body: <p>I have for example a model like this:</p>
  
  <pre><code>class Transaction(models.Model):
      amount = models.FloatField()
      seller = models.ForeignKey(User, related_name='sells', on_delete=models.CASCADE)
      buyer = models.ForeignKey(User, related_name='purchased', on_delete=models.CASCADE)
      created_at = models.DateTimeField(auto_now_add=True)
  </code></pre>
  
  <p>I want to group by all transactions seperated by each date and find some of them. If the <code>created_at</code> is of type <code>DateField</code> I could simply find the count on each day by this query:</p>
  
  <pre><code>Transaction.objects..values('created_at').annotate(count=Count('created_at_date')
  </code></pre>
  
  <p>But this <strong>doesn't work</strong> <code>DateTimeFeilds</code>. </p>
  
  <p>My question is how can i find total count of transactions for each date for this model type.</p>