id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
34058	Widening AutoField to BigAutoField, fails to widen the sequence.	Anders Kaseorg	Mariusz Felisiak	"#30511 changed the behavior of migrations that widen `AutoField`, removing the code that updates the type of the corresponding sequence. This creates a problem in projects that were upgraded from Django 4.0 or earlier, where the `AutoField`s will still be `serial` columns, and then migrated in Django 4.1, where the sequence will not be updated automatically.

Here’s a self-contained reproduction recipe:

1. Install an old version of Django:
   {{{
   #!console
   $ pip install django==4.0.7 psycopg2-binary
   }}}
2. Create a minimal test project:
   {{{
   #!python
   # manage.py
   import os, sys
   from django.core.management import execute_from_command_line
   os.environ.setdefault(""DJANGO_SETTINGS_MODULE"", ""my_settings"")
   execute_from_command_line(sys.argv)
   }}}
   {{{
   #!python
   # my_settings.py
   DATABASES = {
       ""default"": {
           ""ENGINE"": ""django.db.backends.postgresql"",
           ""NAME"": ""my_database"",
       }
   }
   INSTALLED_APPS = [""my_app""]
   }}}
   {{{
   #!python
   # my_app/models.py
   from django.db import models
   class Widget(models.Model):
       id = models.SmallAutoField(primary_key=True)
   }}}
3. Create the PostgreSQL database and run migrations:
   {{{
   #!console
   $ createdb my_database
   $ python manage.py makemigrations my_app 
   Migrations for 'my_app':
     my_app/migrations/0001_initial.py
       - Create model Widget
   $ python manage.py migrate
   Operations to perform:
     Apply all migrations: my_app
   Running migrations:
     Applying my_app.0001_initial... OK
   }}}
4. Upgrade to Django 4.1:
   {{{
   #!console
   $ pip install Django==4.1
   }}}
5. Edit `my_app/models.py` to widen the field from `SmallAutoField` to `BigAutoField`:
   {{{
   #!python
   # my_app/models.py
   from django.db import models
   class Widget(models.Model):
       id = models.BigAutoField(primary_key=True)
   }}}
6. Run migrations:
   {{{
   #!console
   $ ./manage.py makemigrations
   Migrations for 'my_app':
     my_app/migrations/0002_alter_widget_id.py
       - Alter field id on widget
   $ ./manage.py migrate
   Operations to perform:
     Apply all migrations: my_app
   Running migrations:
     Applying my_app.0002_alter_widget_id... OK
   }}}
7. Observe that the field has been widened but the sequence corresponding to it has not:
   {{{
   #!console
   $ ./manage.py dbshell
   psql (14.5, server 13.8)
   Type ""help"" for help.
   
   my_database=> \d my_app_widget
                               Table ""public.my_app_widget""
    Column |  Type  | Collation | Nullable |                  Default                  
   --------+--------+-----------+----------+-------------------------------------------
    id     | bigint |           | not null | nextval('my_app_widget_id_seq'::regclass)
   Indexes:
       ""my_app_widget_pkey"" PRIMARY KEY, btree (id)
   
   my_database=> \d my_app_widget_id_seq
                  Sequence ""public.my_app_widget_id_seq""
      Type   | Start | Minimum | Maximum | Increment | Cycles? | Cache 
   ----------+-------+---------+---------+-----------+---------+-------
    smallint |     1 |       1 |   32767 |         1 | no      |     1
   Owned by: public.my_app_widget.id
   }}}
8. Try and fail to create a large number of rows:
   {{{
   #!console
   $ ./manage.py shell
   Python 3.10.6 (main, Aug  1 2022, 20:38:21) [GCC 11.3.0] on linux
   Type ""help"", ""copyright"", ""credits"" or ""license"" for more information.
   (InteractiveConsole)
   >>> from my_app.models import Widget
   >>> Widget.objects.bulk_create(Widget() for i in range(40000))
   Traceback (most recent call last):
     File ""…/lib/python3.10/site-packages/django/db/backends/utils.py"", line 89, in _execute
       return self.cursor.execute(sql, params)
   psycopg2.errors.SequenceGeneratorLimitExceeded: nextval: reached maximum value of sequence ""my_app_widget_id_seq"" (32767)


   The above exception was the direct cause of the following exception:
   Traceback (most recent call last):
     File ""<console>"", line 1, in <module>
   …
     File ""…/lib/python3.10/site-packages/django/db/backends/utils.py"", line 89, in _execute
       return self.cursor.execute(sql, params)
   django.db.utils.DataError: nextval: reached maximum value of sequence ""my_app_widget_id_seq"" (32767)
   }}}
"	Bug	closed	Database layer (models, ORM)	4.1	Release blocker	fixed		Florian Apolloner Mariusz Felisiak	Accepted	1	0	0	0	0	0