Django "ValueErrror: could not find common ancestor of {migrations}"

Question

I'm trying to follow the documentation in https://docs.djangoproject.com/en/2.0/ref/contrib/postgres/operations/ to create a migration which will essentially perform the SQL statement CREATE EXTENSION IF NOT EXISTS hstore; on the database. I've tried adding the following file, called create_extension_hstore.py, to the migrations directory:

from django.db import migrations
from django.contrib.postgres.operations import CreateExtension


class Migration(migrations.Migration):
    operations = [CreateExtension(name='hstore')]

My 'mental model' of this is that since Django infer the order of the migrations from their dependencies and this one has none, it should be run first. However, I'm getting the error when I try to run python manage.py makemigrations --merge:

(venv) Kurts-MacBook-Pro:lucy-web kurtpeek$ python manage.py makemigrations --merge
(0.000) SELECT typarray FROM pg_type WHERE typname = 'citext'; args=None
(0.003) 
            SELECT c.relname, c.relkind
            FROM pg_catalog.pg_class c
            LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
            WHERE c.relkind IN ('r', 'v')
                AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
                AND pg_catalog.pg_table_is_visible(c.oid); args=None
(0.001) SELECT "django_migrations"."app", "django_migrations"."name" FROM "django_migrations"; args=()
Traceback (most recent call last):
  File "manage.py", line 29, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
    utility.execute()
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/__init__.py", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/commands/makemigrations.py", line 142, in handle
    return self.handle_merge(loader, conflicts)
  File "/Users/kurtpeek/Documents/Dev/lucy/lucy-web/venv/lib/python3.6/site-packages/django/core/management/commands/makemigrations.py", line 272, in handle_merge
    raise ValueError("Could not find common ancestor of %s" % migration_names)
ValueError: Could not find common ancestor of {'0091_family_adopting_or_surrogate', 'create_extension_hstore'}

How can I fix this? I could try adding dependencies=['0001_initial'] to the Migration class but this seems a bit arbitrary as what I actually want is to run this migration before anything else.

Answer 1

I think you would want to add this migration to the dependencies in 0001, if you want it run before the first generated migrations.

If you are just getting to needing hstore now and don't need it to run first you can pretty easily just add as a data migration in place like normal.