From deb561bbe2dbacac32d65272beab3a7708e2c31d Mon Sep 17 00:00:00 2001 From: Víðir Valberg Guðmundsson Date: Sun, 13 Apr 2014 17:18:02 +0200 Subject: Fixed #22422 -- Moved information about the application loading process to refs/applications.txt. --- docs/ref/applications.txt | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) (limited to 'docs/ref') diff --git a/docs/ref/applications.txt b/docs/ref/applications.txt index ddfb883906..01f570a3e7 100644 --- a/docs/ref/applications.txt +++ b/docs/ref/applications.txt @@ -306,3 +306,45 @@ Application registry Raises :exc:`~exceptions.LookupError` if no such application or model exists. Raises :exc:`~exceptions.ValueError` when called with a single argument that doesn't contain exactly one dot. + +.. _application-loading-process: + +Application loading process +=========================== + +Django loads application configurations and models as soon as it starts. Here +are some common problems you may encounter: + +* ``RuntimeError: App registry isn't ready yet.`` This happens when importing + an application configuration or a models module triggers code that depends + on the app registry. + + For example, :func:`~django.utils.translation.ugettext()` uses the app + registry to look up translation catalogs in applications. To translate at + import time, you need :func:`~django.utils.translation.ugettext_lazy()` + instead. (Using :func:`~django.utils.translation.ugettext()` would be a bug, + because the translation would happen at import time, rather than at each + request depending on the active language.) + + Executing database queries with the ORM at import time in models modules + will also trigger this exception. The ORM cannot function properly until all + models are available. + + Another common culprit is :func:`django.contrib.auth.get_user_model()`. Use + the :setting:`AUTH_USER_MODEL` setting to reference the User model at import + time. + +* ``ImportError: cannot import name ...`` This happens if the import sequence + ends up in a loop. + + To eliminate such problems, you should minimize dependencies between your + models modules and do as little work as possible at import time. To avoid + executing code at import time, you can move it into a function and cache its + results. The code will be executed when you first need its results. This + concept is known as "lazy evaluation". + +* ``django.contrib.admin`` will now automatically perform autodiscovery of + ``admin`` modules in installed applications. To prevent it, change your + :setting:`INSTALLED_APPS` to contain + ``'django.contrib.admin.apps.SimpleAdminConfig'`` instead of + ``'django.contrib.admin'``. -- cgit v1.3