Better model 'app_label' introspection using 'INSTALLED_APPS'

[fengb]

Currently, the model generates "app_label" by taking the second to last module:

django.contrib.auth.models.User -> auth
newproj.newapp.models.Newmodel -> newapp
newproj.newapp.models.db.Newmodel -> models

The last example doesn't make any sense. I propose that we match the module chain against 'INSTALLED_APPS' to find the correct app.

[anonymous]

I have an implementation available on Github:

​https://github.com/fengb/django/tree/app-label-introspect

Tests are failing but they look somewhat unrelated. I do not have enough context to fix them.

[fengb]

Crap, I didn't notice that my description formatting gotten eaten...

Middle "paragraph" should be:

• django.contrib.auth.models.User -> auth
• newproj.newapp.models.Newmodel -> newapp
• newproj.newapp.models.db.Newmodel -> models

[Aymeric Augustin]

Your proposal looks correct. But maybe Django should just forbid to define modules outside of <app_label>.models — this deserves a bit more investigation.

Maybe we should raise an error when app_label isn't in INSTALLED_APPS. Currently it's possible to import models from an app that isn't in INSTALLED_APPS, and it can lead to hard-to-debug errors. This is related to the app-refactor project — see #3591.

[Aymeric Augustin]

I just remembered that Django provide an option exactly for this:

​https://docs.djangoproject.com/en/dev/ref/models/options/#app-label