Fixed #15309 -- reST/Sphinx cleanup on the ContentTypes Framework docs.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@15544 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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Gabriel Hurley
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@ -5,8 +5,8 @@ The contenttypes framework
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.. module:: django.contrib.contenttypes
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:synopsis: Provides generic interface to installed models.
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Django includes a :mod:`contenttypes` application that can track all of
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the models installed in your Django-powered project, providing a
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Django includes a :mod:`~django.contrib.contenttypes` application that can
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track all of the models installed in your Django-powered project, providing a
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high-level, generic interface for working with your models.
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Overview
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@ -54,34 +54,37 @@ installed; several of Django's other bundled applications require it:
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* Django's comments system (:mod:`django.contrib.comments`) uses it to
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"attach" comments to any installed model.
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.. currentmodule:: django.contrib.contenttypes.models
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The ``ContentType`` model
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=========================
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.. class:: models.ContentType
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.. class:: ContentType
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Each instance of :class:`~django.contrib.contenttypes.models.ContentType`
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has three fields which, taken together, uniquely describe an installed model:
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has three fields which, taken together, uniquely describe an installed
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model:
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.. attribute:: models.ContentType.app_label
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.. attribute:: app_label
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The name of the application the model is part of. This is taken from
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the :attr:`app_label` attribute of the model, and includes only the *last*
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part of the application's Python import path;
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"django.contrib.contenttypes", for example, becomes an :attr:`app_label`
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of "contenttypes".
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the :attr:`app_label` attribute of the model, and includes only the
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*last* part of the application's Python import path;
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"django.contrib.contenttypes", for example, becomes an
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:attr:`app_label` of "contenttypes".
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.. attribute:: models.ContentType.model
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.. attribute:: model
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The name of the model class.
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.. attribute:: models.ContentType.name
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.. attribute:: name
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The human-readable name of the model. This is taken from the
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:attr:`verbose_name <django.db.models.fields.Field.verbose_name>`
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:attr:`verbose_name <django.db.models.Field.verbose_name>`
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attribute of the model.
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Let's look at an example to see how this works. If you already have
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the contenttypes application installed, and then add
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the :mod:`~django.contrib.contenttypes` application installed, and then add
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:mod:`the sites application <django.contrib.sites>` to your
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:setting:`INSTALLED_APPS` setting and run ``manage.py syncdb`` to install it,
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the model :class:`django.contrib.sites.models.Site` will be installed into
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@ -89,33 +92,34 @@ your database. Along with it a new instance of
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:class:`~django.contrib.contenttypes.models.ContentType` will be
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created with the following values:
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* :attr:`app_label` will be set to ``'sites'`` (the last part of the Python
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* :attr:`~django.contrib.contenttypes.models.ContentType.app_label`
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will be set to ``'sites'`` (the last part of the Python
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path "django.contrib.sites").
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* :attr:`model` will be set to ``'site'``.
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* :attr:`~django.contrib.contenttypes.models.ContentType.model`
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will be set to ``'site'``.
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* :attr:`name` will be set to ``'site'``.
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* :attr:`~django.contrib.contenttypes.models.ContentType.name`
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will be set to ``'site'``.
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.. _the verbose_name attribute: ../model-api/#verbose_name
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Methods on ``ContentType`` instances
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====================================
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.. class:: models.ContentType
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Each :class:`~django.contrib.contenttypes.models.ContentType` instance has
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methods that allow you to get from a
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:class:`~django.contrib.contenttypes.models.ContentType` instance to the
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model it represents, or to retrieve objects from that model:
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Each :class:`~django.contrib.contenttypes.models.ContentType` instance has
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methods that allow you to get from a
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:class:`~django.contrib.contenttypes.models.ContentType` instance to the model
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it represents, or to retrieve objects from that model:
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.. method:: models.ContentType.get_object_for_this_type(**kwargs)
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.. method:: ContentType.get_object_for_this_type(**kwargs)
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Takes a set of valid :ref:`lookup arguments <field-lookups-intro>` for the
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model the :class:`~django.contrib.contenttypes.models.ContentType`
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represents, and does :lookup:`a get() lookup <get>` on that model,
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returning the corresponding object.
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represents, and does :meth:`a get() lookup <django.db.models.QuerySet.get>`
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on that model, returning the corresponding object.
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.. method:: models.ContentType.model_class()
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.. method:: ContentType.model_class()
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Returns the model class represented by this
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:class:`~django.contrib.contenttypes.models.ContentType` instance.
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@ -129,7 +133,8 @@ For example, we could look up the
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>>> user_type
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<ContentType: user>
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And then use it to query for a particular ``User``, or to get access
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And then use it to query for a particular
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:class:`~django.contrib.auth.models.User`, or to get access
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to the ``User`` model class::
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>>> user_type.model_class()
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@ -139,15 +144,15 @@ to the ``User`` model class::
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Together,
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:meth:`~django.contrib.contenttypes.models.ContentType.get_object_for_this_type`
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and :meth:`~django.contrib.contenttypes.models.ContentType.model_class`
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enable two extremely important use cases:
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and :meth:`~django.contrib.contenttypes.models.ContentType.model_class` enable
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two extremely important use cases:
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1. Using these methods, you can write high-level generic code that
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performs queries on any installed model -- instead of importing and using
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a single specific model class, you can pass an ``app_label`` and
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``model`` into a :class:`~django.contrib.contenttypes.models.ContentType`
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lookup at runtime, and then work with the model class or retrieve objects
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from it.
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performs queries on any installed model -- instead of importing and
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using a single specific model class, you can pass an ``app_label`` and
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``model`` into a
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:class:`~django.contrib.contenttypes.models.ContentType` lookup at
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runtime, and then work with the model class or retrieve objects from it.
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2. You can relate another model to
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:class:`~django.contrib.contenttypes.models.ContentType` as a way of
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@ -156,7 +161,7 @@ enable two extremely important use cases:
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Several of Django's bundled applications make use of the latter technique.
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For example,
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:class:`the permissions system <django.contrib.auth.models.Permission` in
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:class:`the permissions system <django.contrib.auth.models.Permission>` in
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Django's authentication framework uses a
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:class:`~django.contrib.auth.models.Permission` model with a foreign
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key to :class:`~django.contrib.contenttypes.models.ContentType`; this lets
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@ -166,36 +171,40 @@ key to :class:`~django.contrib.contenttypes.models.ContentType`; this lets
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The ``ContentTypeManager``
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--------------------------
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.. class:: models.ContentTypeManager
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.. class:: ContentTypeManager
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:class:`~django.contrib.contenttypes.models.ContentType` also has a custom
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manager, :class:`~django.contrib.contenttypes.models.ContentTypeManager`,
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which adds the following methods:
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.. method:: models.ContentTypeManager.clear_cache()
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.. method:: clear_cache()
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Clears an internal cache used by
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:class:`~django.contrib.contenttypes.models.ContentType` to keep track
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of which models for which it has created
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:class:`django.contrib.contenttypes.models.ContentType` instances. You
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:class:`~django.contrib.contenttypes.models.ContentType` instances. You
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probably won't ever need to call this method yourself; Django will call
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it automatically when it's needed.
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.. method:: models.ContentTypeManager.get_for_model(model)
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.. method:: get_for_model(model)
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Takes either a model class or an instance of a model, and returns the
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:class:`~django.contrib.contenttypes.models.ContentType` instance
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representing that model.
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The :meth:`~models.ContentTypeManager.get_for_model()` method is especially useful when you know you
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need to work with a :class:`ContentType <django.contrib.contenttypes.models.ContentType>` but don't want to go to the
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trouble of obtaining the model's metadata to perform a manual lookup::
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The :meth:`~ContentTypeManager.get_for_model()` method is especially
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useful when you know you need to work with a
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:class:`ContentType <django.contrib.contenttypes.models.ContentType>` but don't
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want to go to the trouble of obtaining the model's metadata to perform a manual
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lookup::
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>>> from django.contrib.auth.models import User
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>>> user_type = ContentType.objects.get_for_model(User)
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>>> user_type
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<ContentType: user>
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.. module:: django.contrib.contenttypes.generic
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.. _generic-relations:
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Generic relations
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@ -224,23 +233,25 @@ A simple example is a tagging system, which might look like this::
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def __unicode__(self):
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return self.tag
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A normal :class:`~django.db.models.fields.related.ForeignKey` can only "point
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A normal :class:`~django.db.models.ForeignKey` can only "point
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to" one other model, which means that if the ``TaggedItem`` model used a
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:class:`~django.db.models.fields.related.ForeignKey` it would have to
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:class:`~django.db.models.ForeignKey` it would have to
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choose one and only one model to store tags for. The contenttypes
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application provides a special field type --
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:class:`django.contrib.contenttypes.generic.GenericForeignKey` -- which
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application provides a special field type which
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works around this and allows the relationship to be with any
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model. There are three parts to setting up a
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:class:`~django.contrib.contenttypes.generic.GenericForeignKey`:
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model:
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1. Give your model a :class:`~django.db.models.fields.related.ForeignKey`
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.. class:: GenericForeignKey
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There are three parts to setting up a
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:class:`~django.contrib.contenttypes.generic.GenericForeignKey`:
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1. Give your model a :class:`~django.db.models.ForeignKey`
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to :class:`~django.contrib.contenttypes.models.ContentType`.
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2. Give your model a field that can store a primary-key value from the
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models you'll be relating to. (For most models, this means an
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:class:`~django.db.models.fields.IntegerField` or
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:class:`~django.db.models.fields.PositiveIntegerField`.)
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2. Give your model a field that can store primary key values from the
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models you'll be relating to. For most models, this means a
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:class:`~django.db.models.PositiveIntegerField`.
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This field must be of the same type as the primary key of the models
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that will be involved in the generic relation. For example, if you use
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@ -257,7 +268,7 @@ model. There are three parts to setting up a
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look for.
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This will enable an API similar to the one used for a normal
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:class:`~django.db.models.fields.related.ForeignKey`;
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:class:`~django.db.models.ForeignKey`;
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each ``TaggedItem`` will have a ``content_object`` field that returns the
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object it's related to, and you can also assign to that field or use it when
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creating a ``TaggedItem``::
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@ -271,8 +282,9 @@ creating a ``TaggedItem``::
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Due to the way :class:`~django.contrib.contenttypes.generic.GenericForeignKey`
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is implemented, you cannot use such fields directly with filters (``filter()``
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and ``exclude()``, for example) via the database API. They aren't normal field
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objects. These examples will *not* work::
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and ``exclude()``, for example) via the database API. Because a
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:class:`~django.contrib.contenttypes.generic.GenericForeignKey` isn't a
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normal field objects, these examples will *not* work::
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# This will fail
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>>> TaggedItem.objects.filter(content_object=guido)
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@ -282,6 +294,8 @@ objects. These examples will *not* work::
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Reverse generic relations
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-------------------------
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.. class:: GenericRelation
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If you know which models you'll be using most often, you can also add
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a "reverse" generic relationship to enable an additional API. For example::
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@ -301,17 +315,20 @@ be used to retrieve their associated ``TaggedItems``::
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>>> b.tags.all()
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[<TaggedItem: django>, <TaggedItem: python>]
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Just as :class:`django.contrib.contenttypes.generic.GenericForeignKey`
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Just as :class:`~django.contrib.contenttypes.generic.GenericForeignKey`
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accepts the names of the content-type and object-ID fields as
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arguments, so too does ``GenericRelation``; if the model which has the
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generic foreign key is using non-default names for those fields, you
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must pass the names of the fields when setting up a
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``GenericRelation`` to it. For example, if the ``TaggedItem`` model
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arguments, so too does
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:class:`~django.contrib.contenttypes.generic.GenericRelation`;
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if the model which has the generic foreign key is using non-default names
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for those fields, you must pass the names of the fields when setting up a
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:class:`.GenericRelation` to it. For example, if the ``TaggedItem`` model
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referred to above used fields named ``content_type_fk`` and
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``object_primary_key`` to create its generic foreign key, then a
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``GenericRelation`` back to it would need to be defined like so::
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:class:`.GenericRelation` back to it would need to be defined like so::
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tags = generic.GenericRelation(TaggedItem, content_type_field='content_type_fk', object_id_field='object_primary_key')
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tags = generic.GenericRelation(TaggedItem,
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content_type_field='content_type_fk',
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object_id_field='object_primary_key')
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Of course, if you don't add the reverse relationship, you can do the
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same types of lookups manually::
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@ -362,37 +379,39 @@ might be tempted to try something like::
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Bookmark.objects.aggregate(Count('tags'))
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This will not work correctly, however. The generic relation adds extra filters
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to the queryset to ensure the correct content type, but the ``aggregate`` method
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doesn't take them into account. For now, if you need aggregates on generic
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relations, you'll need to calculate them without using the aggregation API.
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to the queryset to ensure the correct content type, but the
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:meth:`~django.db.models.QuerySet.aggregate` method doesn't take them into
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account. For now, if you need aggregates on generic relations, you'll need
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to calculate them without using the aggregation API.
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Generic relations in forms and admin
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------------------------------------
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:mod:`django.contrib.contenttypes.generic` provides
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The :mod:`django.contrib.contenttypes.generic` module provides
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:class:`~django.contrib.contenttypes.generic.GenericInlineFormSet`,
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:class:`~django.contrib.contenttypes.generic.GenericTabularInline`
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and :class:`~django.contrib.contenttypes.generic.GenericStackedInline`
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(the last two subclasses of :class:`~django.contrib.contenttypes.generic.GenericInlineModelAdmin`).
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(the last two are subclasses of
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:class:`~django.contrib.contenttypes.generic.GenericInlineModelAdmin`).
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This enables the use of generic relations in forms and the admin. See the
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:doc:`model formset </topics/forms/modelforms>` and
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:ref:`admin <using-generic-relations-as-an-inline>` documentation for more
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information.
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.. class:: generic.GenericInlineModelAdmin
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.. class:: GenericInlineModelAdmin
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The :class:`~django.contrib.contenttypes.generic.GenericInlineModelAdmin`
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class inherits all properties from an
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:class:`~django.contrib.admin.InlineModelAdmin` class. However,
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it adds a couple of its own for working with the generic relation:
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.. attribute:: generic.GenericInlineModelAdmin.ct_field
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.. attribute:: ct_field
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The name of the
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:class:`~django.contrib.contenttypes.models.ContentType` foreign key
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field on the model. Defaults to ``content_type``.
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.. attribute:: generic.GenericInlineModelAdmin.ct_fk_field
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.. attribute:: ct_fk_field
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The name of the integer field that represents the ID of the related
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object. Defaults to ``object_id``.
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