better way to query in django

Question

Is there a better way to do this

questionobjects = Questions.objects.all()
for questionobject in questionobjects:
        answerobjects = Answers.objects.filter(question=questionobject.id).count()

In the above query Answers model has foreign key relation with Questions. But in the above script the query Answer query executes based on the number of questionobjects.

Suppose there are 10 questionobjects then 10 separate answerobject queries take place. Is there a way to do this with a single query because as the number of questionobjects increases, it will be a problem because the number of answerobjects queries also increase

Daniel Roseman · Accepted Answer · 2012-06-07 11:10:03Z

6

So it looks like you just care about the count of answers, rather than getting the actual answer objects. You can do this with annotations:

from django.db.models import Count
Question.objects.all().annotate(Count('answers'))

answered Jun 7, 2012 at 11:10

Daniel Roseman

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4 Comments

Ching Chong Over a year ago

how to write the above query to get questionobjects whose answers count is greater than 3

Ching Chong Over a year ago

i know how do that using a sql query but iam new to django and have issues with it

DrTyrsa Over a year ago

@ChingChong docs.djangoproject.com/en/dev/topics/db/aggregation/…

Sindri Guðmundsson Over a year ago

@ChingChong Questions.objects.annotate(count=Count('answers')).filter(count__gt=3)

Sindri Guðmundsson · Accepted Answer · 2012-06-07 11:10:57Z

4

Take a look at annotation: Django Annotation

from django.db.models import Count
questions = Questions.objects.annotate(count=Count('answers'))

Then you can access the count with [q.count for q in questions]

answered Jun 7, 2012 at 11:10

Sindri Guðmundsson

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