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ba7206cd81
Returning None on errors required unpythonic error checking and was inconsistent with get_app_config. get_model was a private API until the previous commit, but given that it was certainly used in third party software, the change is explained in the release notes. Applied the same change to get_registered_model, which is a new private API introduced during the recent refactoring.
207 lines
6.8 KiB
Plaintext
207 lines
6.8 KiB
Plaintext
============
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Applications
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============
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.. module:: django.apps
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.. versionadded:: 1.7
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Django contains a registry of installed applications that stores configuration
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and provides introspection. It also maintains a list of available :doc:`models
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</topics/db/models>`.
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This registry is simply called :attr:`~django.apps.apps` and it's available in
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:mod:`django.apps`::
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>>> from django.apps import apps
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>>> apps.get_app_config('admin').verbose_name
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'Admin'
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Projects and applications
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=========================
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Django has historically used the term **project** to describe an installation
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of Django. A project is defined primarily by a settings module.
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The term **application** describes a Python package that provides some set of
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features. Applications may be reused in various projects.
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.. note::
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This terminology is somewhat confusing these days as it became common to
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use the phrase "web app" to describe what equates to a Django project.
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Applications include some combination of models, views, templates, template
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tags, static files, URLs, middleware, etc. They're generally wired into
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projects with the :setting:`INSTALLED_APPS` setting and optionally with other
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mechanisms such as URLconfs, the :setting:`MIDDLEWARE_CLASSES` setting, or
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template inheritance.
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It is important to understand that a Django application is just a set of code
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that interacts with various parts of the framework. There's no such thing as
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an ``Application`` object. However, there's a few places where Django needs to
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interact with installed applications, mainly for configuration and also for
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introspection. That's why the application registry maintains metadata in an
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:class:`~django.apps.AppConfig` instance for each installed application.
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Configuring applications
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========================
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To configure an application, subclass :class:`~django.apps.AppConfig` and put
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the dotted path to that subclass in :setting:`INSTALLED_APPS`.
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Django uses the default :class:`~django.apps.AppConfig` class when
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:setting:`INSTALLED_APPS` simply contains the dotted path to an application
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module.
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For application authors
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-----------------------
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If you're creating a pluggable app called "Rock ’n’ roll", here's how you
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would provide a proper name for the admin::
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# rock_n_roll/app.py
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from django.apps import AppConfig
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class RockNRollConfig(AppConfig):
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name = 'rock_n_roll'
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verbose_name = "Rock ’n’ roll"
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You would then tell your users to add ``'rock_n_roll.app.RockNRollConfig'`` to
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their :setting:`INSTALLED_APPS`.
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The recommended convention is to put the configuration class in a submodule of
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the application called ``app``. However, this isn't enforced by Django.
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You must include the :attr:`~django.apps.AppConfig.name` attribute for Django
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to determine which application this configuration applies to. You can define
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any attributes documented in the :class:`~django.apps.AppConfig` API
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reference.
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For application users
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---------------------
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If you're using "Rock ’n’ roll" in a project called ``anthology``, but you
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want it to show up as "Gypsy jazz" instead, you can provide your own
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configuration::
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# anthology/apps.py
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from rock_n_roll.app import RockNRollConfig
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class GypsyJazzConfig(RockNRollConfig):
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verbose_name = "Gypsy jazz"
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# anthology/settings.py
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INSTALLED_APPS = [
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'anthology.apps.GypsyJazzConfig',
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# ...
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]
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Again, defining project-specific configuration classes in a submodule called
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``apps`` is a convention, not a requirement.
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Application configuration
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=========================
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.. class:: AppConfig
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Application configuration objects store metadata for an application. Some
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attributes can be configured in :class:`~django.apps.AppConfig`
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subclasses. Others are set by Django and read-only.
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Configurable attributes
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-----------------------
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.. attribute:: AppConfig.verbose_name
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Human-readable name for the application, e.g. "Admin".
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If this isn't provided, Django uses ``label.title()``.
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Read-only attributes
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--------------------
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.. attribute:: AppConfig.name
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Full Python path to the application, e.g. ``'django.contrib.admin'``.
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.. attribute:: AppConfig.label
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Last component of the Python path to the application, e.g. ``'admin'``.
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This value must be unique across a Django project.
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.. attribute:: AppConfig.path
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Filesystem path to the application directory, e.g.
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``'/usr/lib/python2.7/dist-packages/django/contrib/admin'``.
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It may be ``None`` if the application isn't stored in a directory, for
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instance if it's loaded from an egg.
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.. attribute:: AppConfig.module
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Root module for the application, e.g. ``<module 'django.contrib.admin' from
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'django/contrib/admin/__init__.pyc'>``.
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.. attribute:: AppConfig.models_module
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Module containing the models, e.g. ``<module 'django.contrib.admin.models'
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from 'django/contrib/admin/models.pyc'>``.
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It may be ``None`` if the application doesn't contain a ``models`` module.
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Methods
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-------
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.. method:: AppConfig.get_model(model_name)
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Returns the :class:`~django.db.models.Model` with the given
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``model_name``. Raises :exc:`~exceptions.LookupError` if no such model
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exists. ``model_name`` is case-insensitive.
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Application registry
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====================
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.. data:: apps
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The application registry provides the following public API. Methods that
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aren't listed below are considered private and may change without notice.
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.. method:: apps.ready()
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Returns ``True`` if the registry is fully populated.
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.. method:: apps.get_app_configs(only_with_models_module=False)
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Returns an iterable of :class:`~django.apps.AppConfig` instances.
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If only applications containing a models module are of interest, this method
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can be called with ``only_with_models_module=True``.
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.. method:: apps.get_app_config(app_label, only_with_models_module=False)
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Returns an :class:`~django.apps.AppConfig` for the application with the
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given ``app_label``. Raises :exc:`~exceptions.LookupError` if no such
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application exists.
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If only applications containing a models module are of interest, this method
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can be called with ``only_with_models_module=True``.
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.. method:: apps.has_app(app_name)
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Checks whether an application with the given name exists in the registry.
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``app_name`` is the full name of the app, e.g. 'django.contrib.admin'.
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Unlike :meth:`~django.apps.apps.get_app_config`, this method can be called
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safely at import time. If the registry is still being populated, it may
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return ``False``, even though the app will become available later.
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.. method:: apps.get_model(app_label, model_name)
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Returns the :class:`~django.db.models.Model` with the given ``app_label``
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and ``model_name``. Raises :exc:`~exceptions.LookupError` if no such
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application or model exists. ``model_name`` is case-insensitive.
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