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Fixed #24305 -- Allowed overriding fields on abstract models.

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Fields inherited from abstract base classes may be overridden like
any other Python attribute. Inheriting from multiple models/classes
with the same attribute name will follow the MRO.
This commit is contained in:
Aron Podrigal
2015-08-03 08:03:41 -04:00
committed by Tim Graham
parent 61a16e0270
commit 85ef98dc6e
5 changed files with 443 additions and 33 deletions
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34
docs/topics/db/models.txt
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@@ -1376,11 +1376,35 @@ Field name "hiding" is not permitted
-------------------------------------
In normal Python class inheritance, it is permissible for a child class to
override any attribute from the parent class. In Django, this is not permitted
for attributes that are :class:`~django.db.models.Field` instances (at
least, not at the moment). If a base class has a field called ``author``, you
cannot create another model field called ``author`` in any class that inherits
from that base class.
override any attribute from the parent class. In Django, this isn't usually
permitted for model fields. If a non-abstract model base class has a field
called ``author``, you can't create another model field or define
an attribute called ``author`` in any class that inherits from that base class.
This restriction doesn't apply to model fields inherited from an abstract
model. Such fields may be overridden with another field or value, or be removed
by setting ``field_name = None``.
.. versionchanged:: 1.10
The ability to override abstract fields was added.
.. warning::
Model managers are inherited from abstract base classes. Overriding an
inherited field which is referenced by an inherited
:class:`~django.db.models.Manager` may cause subtle bugs. See :ref:`custom
managers and model inheritance <custom-managers-and-inheritance>`.
.. note::
Some fields define extra attributes on the model, e.g. a
:class:`~django.db.models.ForeignKey` defines an extra attribute with
``_id`` appended to the field name, as well as ``related_name`` and
``related_query_name`` on the foreign model.
These extra attributes cannot be overridden unless the field that defines
it is changed or removed so that it no longer defines the extra attribute.
Overriding fields in a parent model leads to difficulties in areas such as
initializing new instances (specifying which field is being initialized in