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Python Django ORM Total Control Aggregate

Mirko Xiang Zhao
Mirko Xiang Zhao
17,787 Points
Posted by Mirko Xiang Zhao
Mirko Xiang Zhao
17,787 Points

Django ORM Avg aggregation

I am stuck with more challenge, just missing this one to complete the course and get a shiny new badge. Thanks for the help!

products/utils.py 
from django.db.models import Avg

from . import models


def current_average():
    reviews = models.Review.objects.annotate(
        average = Avg('rating')
    )

    average = reviews.aggregate(average=Avg('average'))

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

You are very close. Two errors:

  • Your current code does not return the average result, and
  • reusing average as the annotation and aggregate appears to interfere with the results
def current_average():
    reviews = models.Review.objects.annotate(
        r_average = Avg('rating')  # <-- changed to 'r_average'
    )
    average = reviews.aggregate(average=Avg('r_average'))  # <-- changed to 'r_average'
    return average  # <-- add return statement

While this passes, it is adding an unnecessary step by creating the annotation first. Since each review has but one rating, the average or "r_average" will be the same value as the rating. You can skip the annotation and go directly to the aggregation:

def current_average():
    average = models.Review.objects.aggregate(average=Avg('rating'))
    return average
Arindam Roychowdhury
Arindam Roychowdhury
3,244 Points
Arindam Roychowdhury
Arindam Roychowdhury
3,244 Points 
def current_average():
    reviews = models.Review.objects.all()
    average = reviews.aggregate(average=Avg('rating'))
    return average