Allow to create models with static app_label at import stage.

[Jakub Skiepko]

I have submited PR with this change. ​https://github.com/django/django/pull/6163
As I understand it django discourage importing models before all apps are initialized only because model need to know its 'app_label'.
If app_label is provided in class Meta it should be ok, but it still raises exception.

[Aymeric Augustin]

As I understand it django discourage importing models before all apps are initialized only because model need to know its 'app_label'.

This is quite far from being the whole story. Have a look at the mailing list discussions about app-loading and at my talk at DjangoCon Europe 2014 for an explanation of why Django needs to keep a consistent registry of models.

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This change seems consistent with my intent here: https://code.djangoproject.com/ticket/21680#comment:4.

However I still want to increase consistency of the app registry: https://code.djangoproject.com/ticket/21682.

This would enforce the requirement that models live in an app and are imported after their app.

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Can you clarify the use case for this change? I'm not sure it's a good thing to relax this check.

I suspect it could reopen some of the bugs the app-loading refactor fixed.

[Jakub Skiepko]

My use case is probably silly and not worth of braking your constraints, but I believe this PR does not break one about consistency of app registry - it just lets you do what could do anyway but earlier. The other constraint about importing models after apps is not documented properly and I didn't knew about it. ref: ​https://docs.djangoproject.com/en/1.9/ref/applications/#how-applications-are-loaded ("Strictly speaking, Django allows importing models once their application configuration is loaded")

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In my opinion it is not consistient, that models have to magicaly install themselves in metaclass while applications are installed manualy using INSTALLED_APPS. If it was the app who installs models using in example self.installed_models you wouldn't need any additional constraints about import order.

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My use case: In my projects i like to have "external api" of application in init.py Sadly lots of this api uses models. It is just a way to have "import models" statement in my init.py, apps.py and every module they importing from on module level and not copied to every function there which obscures readability. I would rather explicit assign app_labels to my models.

[Aymeric Augustin]

The ability to import models (directly or indirectly) in an application's __init__.py was deprecated in 1.7 and removed in 1.9. I knew it would make your use case impossible. Importing too many things in __init__.py can cause hard-to-break import loops. That's why I didn't mind discouraging this pattern.

The current situation results from trade-off between fixing very complex bugs that could occur when a Django application starts and preserving backwards-compatibility. It was done for reasons discussed at length on the mailing list.

I don't oppose further changes in the area, however, I kindly ask that you review past discussions (search for "app-loading" on the django-developers archives) before undoing decisions into which a lot of work was put. Thanks.

PS -- regarding the fact that apps are explicitly declared while models aren't, Django has always had an INSTALLED_APPS setting but never had INSTALLED_MODELS or equivalent, so I don't think you can draw useful conclusions from this observation.

[Tim Graham]

Closing pending further investigation by the reporter.