Fields.E323 check for mixing python & database-level on_delete values not checked on implicit M2M through tables

[Jacob Walls]

This set of models with an explicit through= model raises Fields.E323 as expected:

from django.contrib.auth.models import User
from django.db import models


class Hobby(models.Model): ...


class Person(models.Model):
    user = models.ForeignKey(User, on_delete=models.DB_CASCADE)
    hobbies = models.ManyToManyField(Hobby, through=HobbyXPerson)


class HobbyXPerson(models.Model):
    hobby = models.ForeignKey(Hobby, on_delete=models.CASCADE)
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    
    class Meta:
        constraints = [
            models.UniqueConstraint(
                fields=["person", "hobby"], name="unique_person_hobby"
            )
        ]

ERRORS:
app.HobbyXPerson.person: (fields.E323) Field specifies Python-level on_delete variant, but referenced model uses database-level variant.
	HINT: Use either database or Python on_delete variants uniformly in the references chain.

But this one does not:

from django.contrib.auth.models import User
from django.db import models


class Hobby(models.Model): ...


class Person(models.Model):
    user = models.ForeignKey(User, on_delete=models.DB_CASCADE)
    hobbies = models.ManyToManyField(Hobby)

Deletions are still collected in python:

def run():
    user = User.objects.create(username='me')
    person = Person.objects.create(user=user)
    person.hobbies.add(Hobby.objects.create())
    person.delete()

DELETE
FROM "app_person_hobbies"
WHERE "app_person_hobbies"."person_id" IN (1)
DELETE
FROM "app_person"
WHERE "app_person"."id" IN (1)

[Mariusz Felisiak]

​PR

[GitHub <noreply@…>]

In c6be0bf:

Fixed #37254 -- Added fields.E323 for models referenced by ManyToManyFields.

Thanks Jacob Walls and Sarah Boyce for reviews.

[Mariusz Felisiak <felisiak.mariusz@…>]

In b26f3c69:

[6.1.x] Fixed #37254 -- Added fields.E323 for models referenced by ManyToManyFields.

Thanks Jacob Walls and Sarah Boyce for reviews.
Backport of c6be0bf3bb744d234947cefd6def9f31d9655800 from main