Django 1.7 initial data can't relies on other apps one.

[Nicals]

In django 1.7, we are told to create initial data using datamigrations instead of fixtures.

But if those initial data depends on other initial data that are created during a post_migrate signal catch we can't access them. Same thing if I need to relies on other apps initial data create on a datamigration : I never know in which order these data are created.

A typical scenario I'm facing:

I need a group spam_user_group that have some django.contrib.admin autogenerated permission in it. I can't relly on python script in datamigration to fetch the Permission I need because their are created within a post_migrate signal.

If I try to create those migrations in my own post_migrate signal handler, I can't be sure that my script will be executed after django.contrib.admin ones.

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Maybe I've misunderstood the documentation about this point, but after a lot of tries and fails I couldn't find a clean way to achieve the scenario I'm presenting here. Maybe this tickets is not a bug, but in this case some documentation about that is to be added.

[Tim Graham]

In the section on ​data migrations, we could describe how to use dependencies to enforce the order in which migrations are executed and link to the section on ​migration dependencies. We should also document the caveat with data created in post_migrate signals as noted in #23422.

[Maxim V]

Hi Nicals, I have exactly same problem. My custom data depends on permissions which created on post migrate hook. The obvious solution is to have some kind of sort, for dispatch_uid for example, of receivers in dispatch/dispatcher.py class Signal, method send. When you can check signals you want to rely on and choose appropriate dispatch_uid for your own connections.
What do you think?

[Prince Verma]

​PR adds the documentation clarification. The documentation build passed, and I checked the rendered page.