Opened 8 years ago

Last modified 8 years ago

#23582 new Cleanup/optimization

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

Reported by: Nicals Owned by: nobody
Component: Documentation Version: 1.7
Severity: Normal Keywords: initial data, migrations
Cc: Triage Stage: Accepted
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no


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.


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.

Change History (2)

comment:1 Changed 8 years ago by Tim Graham

Component: MigrationsDocumentation
Triage Stage: UnreviewedAccepted
Type: BugCleanup/optimization

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.

comment:2 Changed 8 years ago by 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/ 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?

Last edited 8 years ago by Maxim V (previous) (diff)
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