Create or Update field in Django many-to-many-through model

Question

I want to create_or_update in m-m through model field

This is my models.py

from django.db import models

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

    def __str__(self):
        return self.name

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

    def __str__(self):
        return self.name

class Membership(models.Model):
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    is_featured = models.BooleanField(default=False)
    is_active = models.BooleanField(default=False)

In my view.py Below code is work perfectly fine

person_obj = Person.objects.get(id=1)
group_obj = Group.objects.get(id=1)
group_obj.add(person_obj, through_defaults={'is_featured': False, 'is_active': True})

Now for same group_obj and person_obj I want to update is_featured = True in membership model.

How can i do that? I can do it by filtering Membership table and update fields but i guess it is not a good practice. I wanted to do it by better solution.

I have tried with same line

group_obj.member.add(person_obj, through_defaults={'is_featured': True, 'is_active': True})

but it is not updating that field.

Why do you think "filtering Membership table and update fields" is not the right answer? On the contrary, that is exactly what you should do: `Membership.objects.filter(group=group_obj, person=person_obj).update(is_featured=True)`. — Daniel Roseman, Nov 15 '19 at 12:13
@DanielRoseman It will work. but I am searching for better way to do it like update_or_create. — Somil, Nov 15 '19 at 12:23
@Somil: the problem is that you do not want `is_active` to be updated I think? — Willem Van Onsem, Nov 15 '19 at 12:24
no , it depends on request data, if is_active is present in request data then it should be update. — Somil, Nov 15 '19 at 12:26
@Somil: given it is not in the request data, and the membership does *not* exist, then what should happen? — Willem Van Onsem, Nov 15 '19 at 12:27
@WillemVanOnsem request data is just like {'is_featured': True, 'is_active': True} — Somil, Nov 15 '19 at 12:30
@Somil: I am trying to reproduce `group_obj.add(person_obj, .....)` but I get: `AttributeError: 'group_ob' object has no attribute 'add'` Did this really work as it is? — Gathide, May 20 '21 at 13:18

score 0 · Answer 1 · answered Nov 15 '19 at 12:31

You can perform an .update_or_create(..) call [Django-doc] on the Membership model:

Membership.objects.update_or_create(
    person_id=person_id,
    group_id=group_id,
    defaults={'is_active': True, 'is_featured': True}
)

Here it will thus make a query where it looks if there already exists a Membership object for the given person_id and group_id. If not, it will construct one, with as values for is_active and is_featured here True (as specified in the defaults). If the Membership object already exists, then it will update both is_active and is_featured to True.

Create or Update field in Django many-to-many-through model

1 Answers1