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How to filter objects for count annotation in Django?

Hello Guys, How are you all? Hope You all Are Fine. Today We Are Going To learn about How to filter objects for count annotation in Django in Python. So Here I am Explain to you all the possible Methods here.

Without wasting your time, Let’s start This Article.

Table of Contents

How to filter objects for count annotation in Django?

  1. How to filter objects for count annotation in Django?

    Conditional aggregation in Django 2.0 allows you to further reduce the amount of faff this has been in the past.

  2. filter objects for count annotation in Django

    Conditional aggregation in Django 2.0 allows you to further reduce the amount of faff this has been in the past.

Method 1

Conditional aggregation in Django 2.0 allows you to further reduce the amount of faff this has been in the past. This will also use Postgres’ filter logic, which is somewhat faster than a sum-case (I’ve seen numbers like 20-30% bandied around).

Anyway, in your case, we’re looking at something as simple as:

from django.db.models import Q, Count
events = Event.objects.annotate(
    paid_participants=Count('participants', filter=Q(participants__is_paid=True))
)

There’s a separate section in the docs about filtering on annotations. It’s the same stuff as conditional aggregation but more like my example above. Either which way, this is a lot healthier than the gnarly subqueries I was doing before.

Method 2

Just discovered that Django 1.8 has new conditional expressions feature, so now we can do like this:

events = Event.objects.all().annotate(paid_participants=models.Sum(
    models.Case(
        models.When(participant__is_paid=True, then=1),
        default=0, output_field=models.IntegerField()
    )))

Conclusion

It’s all About this issue. Hope all Methods helped you a lot. Comment below Your thoughts and your queries. Also, Comment below which Method worked for you? Thank You.

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