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[1.7.x] Fixed #22422 -- Moved information about the application loading process to refs/applications.txt.

Backport of deb561bbe2 from master
This commit is contained in:
Víðir Valberg Guðmundsson 2014-04-13 17:18:02 +02:00 committed by Tim Graham
parent ae15356061
commit bde1bc6672
2 changed files with 44 additions and 35 deletions

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@ -306,3 +306,45 @@ Application registry
Raises :exc:`~exceptions.LookupError` if no such application or model Raises :exc:`~exceptions.LookupError` if no such application or model
exists. Raises :exc:`~exceptions.ValueError` when called with a single exists. Raises :exc:`~exceptions.ValueError` when called with a single
argument that doesn't contain exactly one dot. 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'``.

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@ -877,41 +877,8 @@ Start-up sequence
Django 1.7 loads application configurations and models as soon as it starts. Django 1.7 loads application configurations and models as soon as it starts.
While this behavior is more straightforward and is believed to be more robust, While this behavior is more straightforward and is believed to be more robust,
regressions cannot be ruled out. You may encounter the following exceptions: regressions cannot be ruled out. See :ref:`application-loading-process` for
solutions to some 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'``.
Standalone scripts Standalone scripts
^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^