Say I decided to switch from a third party app foo-tags to app bar-tags.
Their Tag models are mostly identical so I just need to move the data from
foo-tag to bar-tag. Since I don't control their migrations, I'd need to
create a migration in one of my own apps:
./manage.py makemigrations my_app --empty
In this migration I'd need to explicitly list the dependencies on these
external apps (otherwise was getting errors that the foo and bar apps were
not available in the app registry):
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
def migrate_tags(apps, schema_editor):
FooTag = apps.get_model('foo_tag', 'FooTag')
BarTag = apps.get_model('bar_tag', 'BarTag')
for old_tag in FooTag.objects.all():
new_tag = BarTag.objects.create(name=old_tag.name)
class Migration(migrations.Migration):
dependencies = [
('my_app', '0001_initial'),
('foo_tag', '0001_initial'),
('bar_tag', '0001_initial'),
]
operations = [
migrations.RunPython(migrate_tags)
]
The migration itself works as expected. However if I now remove foo_tag
from INSTALLED_APPS, Django will now give an error:
KeyError: "Migration my_app.0002_auto_20141212_1951 dependencies reference
nonexistent parent node ('foo_tag', '0001_initial')"
What's the correct way to handle migrating data between 3rd party apps
where one of the apps is eventually removed?
Thanks,
John-Scott
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