On Tue, 2007-04-17 at 08:48 -0700, Andrew Durdin wrote: > On Apr 4, 12:26 pm, Malcolm Tredinnick <[EMAIL PROTECTED]> > wrote: > > > > I cannot think of any reliable way to solve this. It's a reasonably hard > > problem to solve correctly, apparently. I say this because we currently > > are *not* solving it in django/db/models/loading.py when we try to > > initialise a cache of all apps and models. The difficulty is nested > > imports and telling when a module has been fully imported. Our current > > solution works most of the time, but that just makes the occasional > > problem case that much more intrusive. > > As it turns out, my "solution" described above fails when deployed and > not using runserver -- as the signal from the first request is sent > before my app has had a chance to hook it. > > But back to the problem -- would it not be possible for django to > import all installed apps (the __init__.py, and subsequently (if > present) models.py) during its own setup, and make sure they're cached > (e.g. in sys.modules)*? Any app could then do independent > initialisation in its __init__.py module. Django could then send out > a signal to indicate that it's finished loading apps & models, and > anything interested could respond to that (having hooked it in > __init__.py). Could this be a workable approach, do you think? > > [*] Using __init__.py is not at present a good solution, as it can be > executed more than once during django's startup by various > __import__() calls.
The problem is that "import all apps" is not a simple operation and has lots of unexpected (at least until you get used to expecting the unexpected) side-effects. Nested imports are the main cause. :-) The problem is that if application A imports something from application B and application B is also in the list of INSTALLED_APPS (which it would have to be in almost all cases), whilst the import of B is first being done, the sys.modules entry for A will be empty (it will have a key of "A" and a value of None) so that multiple imports don't happen. So anything run when B is imported cannot assume the all the other apps have been fully imported. Cyclic import sequences and even bushy import hierarchies are lots of fun (read "really painful") to handle. I'm currently convinced there are some cases which aren't possible to completely untangle in loading.py, but that may be because I'm not bright enough. However, don't let my negative experiences scare you off. Write a solution and then we can borrow it for loading.py. Regards, Malcolm --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
