Prologue:
This is a question arising often in SO:
- Django Models Group By
- Django equivalent for count and group by
- How to query as GROUP BY in django?
- How to use the ORM for the equivalent of a SQL count, group and join query?
I have composed an example on SO Documentation but since the Documentation will get shut down on August 8, 2017, I will follow the suggestion of this widely upvoted and discussed meta answer and transform my example to a self-answered post.
Of course, I would be more than happy to see any different approach as well!!
Question:
Assume the model:
class Books(models.Model):
title = models.CharField()
author = models.CharField()
price = models.FloatField()
How can I perform the following queries on that model utilizing Django ORM:
GROUP BY ... COUNT
:SELECT author, COUNT(author) AS count FROM myapp_books GROUP BY author
GROUP BY ... SUM
:SELECT author, SUM (price) AS total_price FROM myapp_books GROUP BY author
We can perform a GROUP BY ... COUNT
or a GROUP BY ... SUM
SQL equivalent queries on Django ORM, with the use of annotate()
, values()
, the django.db.models
's Count
and Sum
methods respectfully and optionally the order_by()
method:
GROUP BY ... COUNT:
from django.db.models import Count result = Books.objects.values('author') .order_by('author') .annotate(count=Count('author'))
Now result contains a dictionary with two keys:
author
andcount
:author | count ------------|------- OneAuthor | 5 OtherAuthor | 2 ... | ...
GROUP BY ... SUM:
from django.db.models import Sum result = Books.objects.values('author') .order_by('author') .annotate(total_price=Sum('price'))
Now result contains a dictionary with two columns:
author
andtotal_price
:author | total_price ------------|------------- OneAuthor | 100.35 OtherAuthor | 50.00 ... | ...
来源:https://stackoverflow.com/questions/45547674/how-to-execute-a-group-by-count-or-sum-in-django-orm