django-prefetch_related

models.py

# -*- coding: utf-8 -*-
from django.db import models


class Person(models.Model):
    name = models.CharField(max_length=128)


class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(Person, through='Membership')


class Membership(models.Model):
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    group = models.ForeignKey("Group", on_delete=models.CASCADE)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=64)

    

"""
Shell

In [13]: gs = list(Group.objects.all().prefetch_related('members'))
SELECT `app_group`.`id`,
       `app_group`.`name`
  FROM `app_group`

Execution time: 0.006087s [Database: default]
SELECT (`app_membership`.`group_id`) AS `_prefetch_related_val_group_id`,
       `app_person`.`id`,
       `app_person`.`name`,
       `app_person`.`company_id`
  FROM `app_person`
 INNER JOIN `app_membership`
    ON (`app_person`.`id` = `app_membership`.`person_id`)
 WHERE `app_membership`.`group_id` IN (1, 2)

Execution time: 0.006120s [Database: default]

In [14]: gs
Out[14]: [<Group: Group object (1)>, <Group: Group object (2)>]

In [15]: g = gs[0]

In [16]: g.members
Out[16]: <django.db.models.fields.related_descriptors.create_forward_many_to_many_manager.<locals>.ManyRelatedManager at 0x109742520>

In [17]: g.members.all()
Out[17]: <QuerySet [<Person: Person object (5)>, <Person: Person object (6)>]>
"""

@YukSeungChan
감사합니다!