Specify app dependency in migration

Question

I'm trying to add initial data in Django 1.7 and I've read that it is recommended to use data migrations.

I've created my migration file correctly, called "0001_groups", in which I create few contrib.auth's groups and permissions.

The problem is that it is run before the auth migrations are run.

I went to find out what't the name of the last migration of the auth app, and it's called 0005_alter_user_last_login_null.py. So I tried with:

dependencies = [
    ('auth', '0005_alter_user_last_login_null'),
]

but I get:

KeyError: u"Migration appname.0001_groups dependencies references nonexistent parent node ('auth', '0005_alter_user_last_login_null')"

I've googled that error and it always links to 11 months old fixed bugs of Django.

How can I correctly specify the auth app dependency?

Have you tried `django.contrib.auth` instead of `auth` in specifying dependencies? — Chillar Anand, Sep 06 '14 at 19:31

score 19 · Answer 1 · answered Sep 07 '14 at 00:13

19

I've found out that you can reference the last migration with __latest__:

dependencies = [
    ('auth', '__latest__'),
]

answered Sep 07 '14 at 00:13

Shoe

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In general, though, you don't *want* to reference the latest migration. What if you have a `ForeignKey` to a Model that is later deleted? Your migration will break. It's unlikely to matter with a stable package like `django.contrib.auth` but it's still bad practice and doesn't gain you anything. – Kevin Christopher Henry Sep 07 '14 at 00:37
Not at all, that's not how migrations work. Note that `makemigrations` produces dependencies on *specific* migrations, not `__latest__`, and that the Django source code itself references specific migrations in its dependencies (e.g. [here](https://github.com/django/django/blob/master/django/contrib/flatpages/migrations/0001_initial.py)). For more on the problems with using `__latest__` see [here](https://code.djangoproject.com/ticket/23071). – Kevin Christopher Henry Sep 07 '14 at 01:41
I suggest that you post a new question, along with your code, explaining the problem you're having. There's not enough to go on here. The point about custom `Managers` is explained in the [documentation](https://docs.djangoproject.com/en/dev/topics/migrations/#historical-models). To make migrations work Django has to have a versioned, *textual* representation of your models, and because "it's impossible to serialize arbitrary Python code" that representation can't include custom methods or `Managers`. – Kevin Christopher Henry Sep 07 '14 at 04:43

score 3 · Accepted Answer · answered Sep 06 '14 at 22:31

3

You're using 1.7 but looking at the master source tree. See this and try 0001_initial.

answered Sep 06 '14 at 22:31

Kevin Christopher Henry

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Yeah, I noticed. I ended up using `__latest__`. Thanks. – Shoe Sep 07 '14 at 00:13
2

You can use `__first__` if `0001_initial` is actually what you want. – Rockallite Aug 26 '15 at 09:21

score 0 · Answer 3 · answered Jun 03 '22 at 20:35

In my case, I wanted to depend on the very first migration of whatever the django.conf.setting.AUTH_USER_MODEL is set to, so that I don't have to hard-code the app name in my code.

The following will do just that:

dependencies = [migrations.swappable_dependency(settings.AUTH_USER_MODEL)]

which is equivalent to:

dependencies = [(settings.AUTH_USER_MODEL.rsplit(".")[0], "__first__")]

Specify app dependency in migration

3 Answers3