django implementation group by every two hours,

[kanhaiya yadav]

Hi,

I have a model 
class XyzModel (models.Model):
   name = models.CharField(max_length=NAME_LENGTH)
   unique_id = models.CharField(max_length=NAME_LENGTH)
   info = models.CharField(max_length=NAME_LENGTH, blank=True)
   violation_time = models.DateTimeField()




I have many rows in the database. So I want to group by the results for 
every two hours or for every four hours.
I want the result something like

name                       violation_date                               
interval                                 counts
abc                           2017-07-01                                 
 06:00 - 08:00                           20
xyz                           2017-07-01                                   
08:00 - 10:00                           30

My query is 
XyzModel.objects
            .extra({"day": "date_trunc('hour',violation_time)"}
            .values("day")
            .order_by("day")
            .annotate(count=Count("id"))
But using this query I can only group the result by one hour interval. I 
want to group by more than one hour interval.

Thanks

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