[Django] #35510: migration on_delete=django.db.models.deletion.CASCADE does not create a ON DELETE CASCADE constraint

[Django]

#35510: migration on_delete=django.db.models.deletion.CASCADE does not create a 
ON
DELETE CASCADE constraint
-------------------------------------+-------------------------------------
               Reporter:  Daniel     |          Owner:  nobody
  Ahern                              |
                   Type:  Bug        |         Status:  new
              Component:  Database   |        Version:  5.0
  layer (models, ORM)                |
               Severity:  Normal     |       Keywords:
           Triage Stage:             |      Has patch:  0
  Unreviewed                         |
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 Python 3.12.0 (using a conda environment)
 Django 5.6
 MariaDB/MySQL 8.0.30-0ubuntu0.22.04.1 (Ubuntu)

 models.py:

 {{{
 from django.db import models

 # class TableBoolean(models.Model):
 #     field1 = models.BooleanField(default=False)

 #     class Meta:
 #         db_table = 'test_boolean'

 class Parent(models.Model):
     name = models.CharField(max_length=100)

     def __str__(self):
         return self.name
     class Meta:
         db_table = 'test_parent'

 class Child(models.Model):
     parent = models.ForeignKey(Parent, on_delete=models.CASCADE)
     name = models.CharField(max_length=100)

     def __str__(self):
         return self.name

     class Meta:
         db_table = 'test_child'
 }}}

 Then I do:

 python manage.py makemigrations v506

 which makes:

 {{{
 # Generated by Django 5.0.6 on 2024-06-08 14:09

 import django.db.models.deletion
 from django.db import migrations, models


 class Migration(migrations.Migration):

     initial = True

     dependencies = [
     ]

     operations = [
         migrations.CreateModel(
             name='Parent',
             fields=[
                 ('id', models.BigAutoField(auto_created=True,
 primary_key=True, serialize=False, verbose_name='ID')),
                 ('name', models.CharField(max_length=100)),
             ],
             options={
                 'db_table': 'test_parent',
             },
         ),
         migrations.CreateModel(
             name='Child',
             fields=[
                 ('id', models.BigAutoField(auto_created=True,
 primary_key=True, serialize=False, verbose_name='ID')),
                 ('name', models.CharField(max_length=100)),
                 ('parent',
 models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
 to='v506.parent')),
             ],
             options={
                 'db_table': 'test_child',
             },
         ),
     ]
 }}}

 Running the migration creates a table that does NOT cascade delete:

 {{{
 | test_child | CREATE TABLE `test_child` (
   `id` bigint NOT NULL AUTO_INCREMENT,
   `name` varchar(100) NOT NULL,
   `parent_id` bigint NOT NULL,
   PRIMARY KEY (`id`),
   KEY `test_child_parent_id_e1a9888d_fk_test_parent_id` (`parent_id`),
   CONSTRAINT `test_child_parent_id_e1a9888d_fk_test_parent_id` FOREIGN KEY
 (`parent_id`) REFERENCES `test_parent` (`id`)
 )
 }}}

 Then I test by:
 {{{
 mysql> insert into test_parent(name) values ('test_parent');

 mysql> insert into test_child (name, parent_id) values ('test_child', 1);

 mysql> delete from test_parent where id = 1;
 ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key
 constraint fails (`django506`.`test_child`, CONSTRAINT
 `test_child_parent_id_e1a9888d_fk_test_parent_id` FOREIGN KEY
 (`parent_id`) REFERENCES `test_parent` (`id`))


 }}}

 I am able to alter the table:

 {{{
 ALTER TABLE `test_child`
 DROP FOREIGN KEY `test_child_parent_id_e1a9888d_fk_test_parent_id`;

 ALTER TABLE `test_child`
 ADD CONSTRAINT `test_child_parent_id_e1a9888d_fk_test_parent_id`
 FOREIGN KEY (`parent_id`) REFERENCES `test_parent` (`id`) ON DELETE
 CASCADE;

 mysql> show create table test_child;

 test_child | CREATE TABLE `test_child` (
   `id` bigint NOT NULL AUTO_INCREMENT,
   `name` varchar(100) NOT NULL,
   `parent_id` bigint NOT NULL,
   PRIMARY KEY (`id`),
   KEY `test_child_parent_id_e1a9888d_fk_test_parent_id` (`parent_id`),
   CONSTRAINT `test_child_parent_id_e1a9888d_fk_test_parent_id` FOREIGN KEY
 (`parent_id`) REFERENCES `test_parent` (`id`) ON DELETE CASCADE

 mysql> delete from test_parent where id = 1;
 Query OK, 1 row affected (0.01 sec)

 mysql> select count(*) from test_child;
 +----------+
 | count(*) |
 +----------+
 |        0 |
 +----------+
 1 row in set (0.00 sec)

 }}}

 I would expect ON DELETE CASCADE to be on the table made by the migration
 because the migration has "on_delete=django.db.models.deletion.CASCADE" on
 the line:
 {{{
 ('parent', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
 to='v506.parent')),
 }}}
-- 
Ticket URL: <https://code.djangoproject.com/ticket/35510>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

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