Django does not honor ON DELETE CASCADE

Question

This is my model:

class Subscriber(models.Model):
    ...
    tenant = models.ForeignKey(Tenant, on_delete=models.CASCADE, null=True)
    ...

This is the generated SQL, according to sqlmigrate (and to manual inspection of the database):

ALTER TABLE `myapp_subscriber` ADD CONSTRAINT `myapp_subscriber_tenant_id_b52815ee_fk_myapp_tenant_id` FOREIGN KEY (`tenant_id`) REFERENCES `myapp_tenant` (`id`);

I was expecting something like this:

CREATE TABLE child (
    id INT,
    parent_id INT,
    INDEX par_ind (parent_id),
    FOREIGN KEY (parent_id)
        REFERENCES parent(id)
        ON DELETE CASCADE
) ENGINE=INNODB;

With the ON DELETE CASCADE.

MySql (MariaDB actually) complains when I delete:

SQL Error (1451): Cannot delete or update a parent row: a foreign key constraint fails

Which makes sense since there is no ON DELETE CASCADE clause.

Why is Django 2.1.5 not honoring the ON DELETE CASCADE clause?

Answer 1

From the docs:

on_delete doesn’t create a SQL constraint in the database. Support for database-level cascade options may be implemented later

It will perform the cascade in Django itself, so if you delete a Tenant object using Django delete() your Subscriber object will also be deleted. But not if you do it in SQL.