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 31329 Converting from concrete to abstract inheritance creates invalid migrations Stephen Finucane nobody "I currently have two models using concrete inheritance and would like to split these out into wholly separate tables, dropping the base table in the process. To do this, I have copied all columns from the base table into the ""child"" tables, and would now like to drop the remaining reference to the base table. To do this, I was hoping to (a) add a new auto-incrementing `id` column to the child tables that is not yet a primary key, (b) use a data migration to copy the data from the `parent_ptr_id` column to the `id` column, and (c) drop the `parent_ptr_id` column and switch `id` to be the primary key. However, I've noticed that regardless of what I do, I won't be able to run the migration or generate new migrations because of errors like the below. {{{ Traceback (most recent call last): File ""manage.py"", line 21, in main() File ""manage.py"", line 17, in main execute_from_command_line(sys.argv) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/__init__.py"", line 401, in execute_from_command_line utility.execute() File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/__init__.py"", line 395, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/base.py"", line 328, in run_from_argv self.execute(*args, **cmd_options) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/base.py"", line 369, in execute output = self.handle(*args, **options) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/base.py"", line 83, in wrapped res = handle_func(*args, **kwargs) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/core/management/commands/makemigrations.py"", line 168, in handle migration_name=self.migration_name, File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/autodetector.py"", line 43, in changes changes = self._detect_changes(convert_apps, graph) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/autodetector.py"", line 128, in _detect_changes self.old_apps = self.from_state.concrete_apps File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/state.py"", line 213, in concrete_apps self.apps = StateApps(self.real_apps, self.models, ignore_swappable=True) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/state.py"", line 272, in __init__ self.render_multiple([*models.values(), *self.real_models]) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/state.py"", line 307, in render_multiple model.render(self) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/migrations/state.py"", line 578, in render return type(self.name, bases, body) File ""/tmp/django-error/.venv/lib/python3.7/site-packages/django/db/models/base.py"", line 229, in __new__ base.__name__, django.core.exceptions.FieldError: Local field 'id' in class 'Child' clashes with field of the same name from base class 'Parent'. }}} I suspect this is because the state tracking is not accurately capturing the change in table bases, but I don't know how to override this without faking dropping the entire table and recreating it. I was hoping for an `AlterModelBases` API but there doesn't appear to be one and I'm not sure where to start adding one. Note that I'm taking this approach because the actual model mapping to `Child` holds a lot of data, and I suspect creating a new `Child2` model, copying everything across, and then dropping `Parent` and `Child`, would likely take many hours if not days to do. I would drop down to raw SQL for this but I've yet to figure out how to correctly update the foreign key constraints such that Django can keep track of them. Minimal reproducer below. == Steps to reproduce Create a new project and app. In the app, create the following `models.py`. {{{#!python from django.db import models class Parent(models.Model): pass class Child(Parent): name = models.TextField(blank=True) }}} Create the initial migrations. {{{ $ python manage.py makemigrations Migrations for 'core': core/migrations/0001_initial.py - Create model Parent - Create model Child }}} Modify the `Child` model in `models.py` so that it no longer subclasses `Parent`. {{{#!python from django.db import models class Parent(models.Model): pass class Child(models.Model): name = models.TextField(blank=True) }}} Create the new migrations. You'll be asked to provide a default value for the new `id` column. Provide something arbitrary since we'll be modifying this by hand later to add the data migration: {{{ $ python manage.py makemigrations core You are trying to add a non-nullable field 'id' to child without a default; we can't do that (the database needs something to populate existing rows). Please select a fix: 1) Provide a one-off default now (will be set on all existing rows with a null value for this column) 2) Quit, and let me add a default in models.py Select an option: 1 Please enter the default value now, as valid Python The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now Type 'exit' to exit this prompt >>> 0 Migrations for 'core': core/migrations/0002_auto_20200302_1358.py - Remove field parent_ptr from child - Add field id to child }}} Attempt to check if there are any migrations necessary now. Things will blow up. {{{ $ python manage.py makemigrations core Traceback (most recent call last): File ""manage.py"", line 21, in main() File ""manage.py"", line 17, in main execute_from_command_line(sys.argv) .... }}} This is an issue on 1.11 and 3.0, and presumably everything inbetween." Uncategorized closed Uncategorized 3.0 Normal duplicate Unreviewed 0 0 0 0 0 0