Fixed #14841 -- added xrefs to topics/db/models. Thanks adamv.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14837 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Simon Meers 2010-12-05 23:52:23 +00:00
parent 4800b46746
commit ffa4badbd8
1 changed files with 35 additions and 32 deletions

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@ -115,8 +115,8 @@ determine a few things:
* The database column type (e.g. ``INTEGER``, ``VARCHAR``).
* The widget to use in Django's admin interface, if you care to use it
(e.g. ``<input type="text">``, ``<select>``).
* The :doc:`widget </ref/forms/widgets>` to use in Django's admin interface,
if you care to use it (e.g. ``<input type="text">``, ``<select>``).
* The minimal validation requirements, used in Django's admin and in
automatically-generated forms.
@ -492,9 +492,10 @@ disabled for many-to-many relationships that use an intermediate model.
The only way to create this type of relationship is to create instances of the
intermediate model.
The ``remove`` method is disabled for similar reasons. However, the
``clear()`` method can be used to remove all many-to-many relationships
for an instance::
The :meth:`~django.db.models.fields.related.RelatedManager.remove` method is
disabled for similar reasons. However, the
:meth:`~django.db.models.fields.related.RelatedManager.clear` method can be
used to remove all many-to-many relationships for an instance::
# Beatles have broken up
>>> beatles.members.clear()
@ -972,8 +973,8 @@ right).
So a child model does not have access to its parent's :ref:`Meta
<meta-options>` class. However, there are a few limited cases where the child
inherits behavior from the parent: if the child does not specify an
:attr:`django.db.models.Options.ordering` attribute or a
:attr:`django.db.models.Options.get_latest_by` attribute, it will inherit
:attr:`~django.db.models.Options.ordering` attribute or a
:attr:`~django.db.models.Options.get_latest_by` attribute, it will inherit
these from its parent.
If the parent has an ordering and you don't want the child to have any natural
@ -989,12 +990,12 @@ Inheritance and reverse relations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Because multi-table inheritance uses an implicit
:class:`~django.db.models.fields.OneToOneField` to link the child and
:class:`~django.db.models.OneToOneField` to link the child and
the parent, it's possible to move from the parent down to the child,
as in the above example. However, this uses up the name that is the
default :attr:`~django.db.models.ForeignKey.related_name` value for
:class:`django.db.models.fields.ForeignKey` and
:class:`django.db.models.fields.ManyToManyField` relations. If you
:class:`~django.db.models.ForeignKey` and
:class:`~django.db.models.ManyToManyField` relations. If you
are putting those types of relations on a subclass of another model,
you **must** specify the
:attr:`~django.db.models.ForeignKey.related_name` attribute on each
@ -1002,7 +1003,7 @@ such field. If you forget, Django will raise an error when you run
:djadmin:`validate` or :djadmin:`syncdb`.
For example, using the above ``Place`` class again, let's create another
subclass with a :class:`~django.db.models.fields.ManyToManyField`::
subclass with a :class:`~django.db.models.ManyToManyField`::
class Supplier(Place):
# Must specify related_name on all relations.
@ -1013,11 +1014,11 @@ Specifying the parent link field
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As mentioned, Django will automatically create a
:class:`~django.db.models.fields.OneToOneField` linking your child
:class:`~django.db.models.OneToOneField` linking your child
class back any non-abstract parent models. If you want to control the
name of the attribute linking back to the parent, you can create your
own :class:`~django.db.models.fields.OneToOneField` and set
:attr:`parent_link=True <django.db.models.fields.OneToOneField.parent_link>`
own :class:`~django.db.models.OneToOneField` and set
:attr:`parent_link=True <django.db.models.OneToOneField.parent_link>`
to indicate that your field is the link back to the parent class.
.. _proxy-models:
@ -1045,8 +1046,9 @@ Proxy models are declared like normal models. You tell Django that it's a
proxy model by setting the :attr:`~django.db.models.Options.proxy` attribute of
the ``Meta`` class to ``True``.
For example, suppose you want to add a method to the standard ``User`` model
that will be used in your templates. You can do it like this::
For example, suppose you want to add a method to the standard
:class:`~django.contrib.auth.models.User` model that will be used in your
templates. You can do it like this::
from django.contrib.auth.models import User
@ -1058,37 +1060,38 @@ that will be used in your templates. You can do it like this::
...
The ``MyUser`` class operates on the same database table as its parent
``User`` class. In particular, any new instances of ``User`` will also be
accessible through ``MyUser``, and vice-versa::
:class:`~django.contrib.auth.models.User` class. In particular, any new
instances of :class:`~django.contrib.auth.models.User` will also be accessible
through ``MyUser``, and vice-versa::
>>> u = User.objects.create(username="foobar")
>>> MyUser.objects.get(username="foobar")
<MyUser: foobar>
You could also use a proxy model to define a different default ordering on a
model. The standard ``User`` model has no ordering defined on it
(intentionally; sorting is expensive and we don't want to do it all the time
when we fetch users). You might want to regularly order by the ``username``
attribute when you use the proxy. This is easy::
model. The standard :class:`~django.contrib.auth.models.User` model has no
ordering defined on it (intentionally; sorting is expensive and we don't want
to do it all the time when we fetch users). You might want to regularly order
by the ``username`` attribute when you use the proxy. This is easy::
class OrderedUser(User):
class Meta:
ordering = ["username"]
proxy = True
Now normal ``User`` queries will be unordered and ``OrderedUser`` queries will
be ordered by ``username``.
Now normal :class:`~django.contrib.auth.models.User` queries will be unordered
and ``OrderedUser`` queries will be ordered by ``username``.
QuerySets still return the model that was requested
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There is no way to have Django return, say, a ``MyUser`` object whenever you
query for ``User`` objects. A queryset for ``User`` objects will return those
types of objects. The whole point of proxy objects is that code relying on the
original ``User`` will use those and your own code can use the extensions you
included (that no other code is relying on anyway). It is not a way to replace
the ``User`` (or any other) model everywhere with something of your own
creation.
query for :class:`~django.contrib.auth.models.User` objects. A queryset for
``User`` objects will return those types of objects. The whole point of proxy
objects is that code relying on the original ``User`` will use those and your
own code can use the extensions you included (that no other code is relying on
anyway). It is not a way to replace the ``User`` (or any other) model
everywhere with something of your own creation.
Base class restrictions
~~~~~~~~~~~~~~~~~~~~~~~
@ -1227,5 +1230,5 @@ column name, you can have the same column name appearing in both a child and
an ancestor model for multi-table inheritance (they are columns in two
different database tables).
Django will raise a ``FieldError`` exception if you override any model field
in any ancestor model.
Django will raise a :exc:`~django.core.exceptions.FieldError` if you override
any model field in any ancestor model.