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PODjango aggregate on .extra values
 

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    <p>Model , with abstract base class:</p> <pre><code>class MapObject(models.Model): start_date = models.DateTimeField(default= datetime.strptime('1940-09-01T00:00:00', '%Y-%m-%dT%H:%M:%S')) end_date = models.DateTimeField(default= datetime.strptime('1941-07-01T00:00:00', '%Y-%m-%dT%H:%M:%S')) description = models.TextField(blank=True) location = models.PointField() objects = models.GeoManager() user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add = True) last_modified = models.DateTimeField(auto_now = True) source = models.ForeignKey(Source) address= models.TextField(blank=True, null=True) address_road = models.TextField(blank=True, null=True) class Meta: abstract = True class Bomb(MapObject, BombExtraManager): #Bomb Attributes type = models.CharField(choices= Type_CHOICES, max_length=10) night_bombing = models.BooleanField(blank=True) map_sheet = models.ForeignKey(MapSheet, blank=True, null=True) def __unicode__(self): return self.type </code></pre> <p>Now, I want to get the equivalent result using Django ORM as this query: </p> <pre><code>Select date_part('day',"start_date") as "day", date_part('hour',"start_date") as "hour", Count('id') from "Mapper_bomb" where "source_id" = 1 group by date_part('hour',"start_date"), date_part('day',"start_date") Order by date_part('day',"start_date") ASC, date_part('hour',"start_date") ASC </code></pre> <p>Which would give me a table with the count of bombs per day and hour.</p> <p>Using Django ORM, I have come to the following at the moment (first_day is just a custom manager I defined that returns a subset of the data, same as source_id = 1):</p> <pre><code>Bomb.first_day.extra(select={'date': "date_part(\'day\', \"start_date\")", 'hour': "date_part(\'hour\', \"start_date\")"}).values('date', 'hour').order_by().annotate(Count('date'), Count('hour')) </code></pre> <p>but Django complains FieldError: Cannot resolve keyword 'date' into field. Is there a way using Django ORM to get the desired result or do I need to fallback on raw sql? </p>
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