django.db.utils.IntegrityError: (1452, 'Cannot add or update child row: foreign key constraint failed

Question

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

My model used to look like this.

class Login(models.Model):
    pid              = models.AutoField(primary_key=True)
    custom_username  = models.BooleanField(default=False)
    tnx_hash         = models.CharField(max_length=100, null=True, blank=True)

    def __str__(self):
        return self.username

Then I changed to inheriting from the base admin user model like this.

class Login(User):
    pid              = models.AutoField(primary_key=True)
    custom_username  = models.BooleanField(default=False)
    tnx_hash         = models.CharField(max_length=100, null=True, blank=True)

    def __str__(self):
        return self.username

Now when I run makemigrations and migrate, I get the following error.

Operations to perform:
        Apply all migrations: admin, api, auth, authtoken, contenttypes, sessions
        Running migrations:
        Applying api.0278_auto_20220318_1210...Traceback (most recent call last):
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
            return self.cursor.execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/mysql/base.py", line 73, in execute
            return self.cursor.execute(query, args)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/cursors.py", line 206, in execute
            res = self._query(query)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/cursors.py", line 319, in _query
            db.query(q)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/connections.py", line 259, in query
            _mysql.connection.query(self, query)
        MySQLdb._exceptions.IntegrityError: (1452, 'Cannot add or update a child row: a foreign key constraint fails (`baby`.`#sql-16a7_6a`, CONSTRAINT `api_login_user_ptr_id_7f748092_fk_auth_user_id` FOREIGN KEY (`user_ptr_id`) REFERENCES `auth_user` (`id`))')

        The above exception was the direct cause of the following exception:

        Traceback (most recent call last):
        File "manage.py", line 22, in <module>
            main()
        File "manage.py", line 18, in main
            execute_from_command_line(sys.argv)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
            utility.execute()
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/__init__.py", line 413, in execute
            self.fetch_command(subcommand).run_from_argv(self.argv)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/base.py", line 354, in run_from_argv
            self.execute(*args, **cmd_options)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/base.py", line 398, in execute
            output = self.handle(*args, **options)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/base.py", line 89, in wrapped
            res = handle_func(*args, **kwargs)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/core/management/commands/migrate.py", line 244, in handle
            post_migrate_state = executor.migrate(
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/migrations/executor.py", line 117, in migrate
            state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
            state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
            state = migration.apply(state, schema_editor)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/migrations/migration.py", line 126, in apply
            operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/migrations/operations/fields.py", line 104, in database_forwards
            schema_editor.add_field(
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/mysql/schema.py", line 98, in add_field
            super().add_field(model, field)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/base/schema.py", line 522, in add_field
            self.execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/base/schema.py", line 145, in execute
            cursor.execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 98, in execute
            return super().execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 66, in execute
            return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
            return executor(sql, params, many, context)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
            return self.cursor.execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
            raise dj_exc_value.with_traceback(traceback) from exc_value
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
            return self.cursor.execute(sql, params)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/django/db/backends/mysql/base.py", line 73, in execute
            return self.cursor.execute(query, args)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/cursors.py", line 206, in execute
            res = self._query(query)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/cursors.py", line 319, in _query
            db.query(q)
        File "/Users/soubhagyapradhan/Desktop/upwork/polyverse/polyverse_api/env/lib/python3.8/site-packages/MySQLdb/connections.py", line 259, in query
            _mysql.connection.query(self, query)
        django.db.utils.IntegrityError: (1452, 'Cannot add or update a child row: a foreign key constraint fails (`baby`.`#sql-16a7_6a`, CONSTRAINT `api_login_user_ptr_id_7f748092_fk_auth_user_id` FOREIGN KEY (`user_ptr_id`) REFERENCES `auth_user` (`id`))')

Please take a look. How can I solve this problem safely. Because I have data in my database and the login table is a foreign key to many tables.

ERRORS:
    api.Login.groups: (fields.E304) Reverse accessor for 'api.Login.groups' clashes with reverse accessor for 'auth.User.groups'.
        HINT: Add or change a related_name argument to the definition for 'api.Login.groups' or 'auth.User.groups'.
    api.Login.user_permissions: (fields.E304) Reverse accessor for 'api.Login.user_permissions' clashes with reverse accessor for 'auth.User.user_permissions'.
        HINT: Add or change a related_name argument to the definition for 'api.Login.user_permissions' or 'auth.User.user_permissions'.
    auth.User.groups: (fields.E304) Reverse accessor for 'auth.User.groups' clashes with reverse accessor for 'api.Login.groups'.
        HINT: Add or change a related_name argument to the definition for 'auth.User.groups' or 'api.Login.groups'.
    auth.User.user_permissions: (fields.E304) Reverse accessor for 'auth.User.user_permissions' clashes with reverse accessor for 'api.Login.user_permissions'.
        HINT: Add or change a related_name argument to the definition for 'auth.User.user_permissions' or 'api.Login.user_permissions'.

Answer 1

Inheriting from the User model won't work because it has its own primary key id. You have defined a primary key pid in your Login model. Instead, if you just want to extend the Login model with User fields, you can inherit from the AbstractUser class.

If you want to switch to the Login model as the default user model, you must somehow migrate the data from the auth_user table to the api_login table, using Data migration or SQL, and set AUTH_USER_MODEL = "api.login"