Hi Aymeric, On 09/04/2016 01:03 PM, Aymeric Augustin wrote: > Hello, > > Since Django 1.7, `get_user_model()` cannot be called at import time. > Django contains a lot of methods that start with `UserModel = > get_user_model()` while it would be more natural to declare it as a > global variable in the module. This trips up users and the reason why > it’s forbidden isn’t obvious. ... > However, in many cases, it doesn’t matter whether the model is fully > constructed or not. In the use case I described in my introduction, > the code only needs a reference to the model class at import time; > that reference won’t be used until run time, after the app-loading > process has completed. (Performing SQL queries through the ORM at > import time doesn’t work anyway.) > > For this reason, I think it would make sense to add an API similar to > `apps.get_models()`, but that would work while app-loading is still > in progress. It would make no guarantees about the functionality of > the class it returns until app-loading has completed. > > I implemented a proof of concept here: > https://github.com/django/django/pull/6547.
A few thoughts: 1) A kwarg to `get_model` seems fine, but I don't like the vague FUD of `unsafe=True` (if it's really "not safe" we shouldn't add it / make it public at all). How about something more specific like `require_ready=False`? 2) I think a key question here is the nature and clarity of the problems that arise if you try to make use of an un-ready model class. If the failure mode here is the reintroduction of unpredictable heisenbugs where certain related fields are quietly not present because the model on the other end happens to not have been imported yet, I think that's a strong argument for refraining from introducing this API. Is it possible to make it so that even the model meta introspection APIs (and of course also any attempt to query the db) fail quickly, loudly, and with a clear error message if the app registry is not yet fully populated? If so, then I think there's little risk to adding this API (and in fact I think we could even make it the default behavior of `get_model`). As for whether it's needed in real use, the only feedback I can offer at the moment is that the import-order enforcement that kicked in with the removal of app-loading deprecation shims in Django 1.9 is the primary reason that Instagram has so far upgraded only as far as Django 1.8; fixing the import-order issues appeared to require too much upheaval and would have delayed the upgrade too much. I haven't had time to look closely at those issues so I can't yet offer more detailed feedback on how much the availability of this particular API would help. Carl -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To post to this group, send email to django-developers@googlegroups.com. Visit this group at https://groups.google.com/group/django-developers. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/eabf51d0-712e-32f1-d8e4-320ddf7681ad%40oddbird.net. For more options, visit https://groups.google.com/d/optout.
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