Model Managers

Extend the base Manager class of a model to add/or to modify the initial QuerySet the Manager returns.

There are two main advantages of this:

Clarity: The implementation detail of the filter can be abstracted away, making logic easier to read.
Consistency: The same filter can be reused reducing the risk of differing implementations in the codebase.

managers.py

from django.db import models
from django.db.models.functions import Coalesce
 
class PollManager(models.Manager):
    def with_counts(self):
        return self.annotate(
            num_responses=Coalesce(models.Count("response"), 0)
        )

models.py

from django.db import models
from polls.managers import PollManager
 
class OpinionPoll(models.Model):
    question = models.CharField(max_length=200)
    objects = PollManager()
 
class Response(models.Model):
    poll = models.ForeignKey(OpinionPoll, on_delete=models.CASCADE)

usage.py

OpinionPoll.objects.with_counts()

Components Database Transactions