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

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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1
AUTHORS
View File

@ -69,6 +69,7 @@ answer newbie questions, and generally made Django that much better:
Aram Dulyan
arien <regexbot@gmail.com>
Armin Ronacher
Aron Podrigal <aronp@guaranteedplus.com>
Artem Gnilov <boobsd@gmail.com>
Arthur <avandorp@gmail.com>
Arthur Koziel <http://arthurkoziel.com>

85
django/db/models/base.py
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@ -212,26 +212,35 @@ class ModelBase(type):
if isinstance(field, OneToOneField):
related = resolve_relation(new_class, field.remote_field.model)
parent_links[make_model_tuple(related)] = field
# Track fields inherited from base models.
inherited_attributes = set()
# Do the appropriate setup for any model parents.
for base in parents:
for base in new_class.mro():
original_base = base
if not hasattr(base, '_meta'):
if base not in parents or not hasattr(base, '_meta'):
# Things without _meta aren't functional models, so they're
# uninteresting parents.
inherited_attributes |= set(base.__dict__.keys())
continue
parent_fields = base._meta.local_fields + base._meta.local_many_to_many
# Check for clashes between locally declared fields and those
# on the base classes (we cannot handle shadowed fields at the
# moment).
for field in parent_fields:
if field.name in field_names:
raise FieldError(
'Local field %r in class %r clashes '
'with field of similar name from '
'base class %r' % (field.name, name, base.__name__)
)
if not base._meta.abstract:
# Check for clashes between locally declared fields and those
# on the base classes.
for field in parent_fields:
if field.name in field_names:
raise FieldError(
'Local field %r in class %r clashes with field of '
'the same name from base class %r.' % (
field.name,
name,
base.__name__,
)
)
else:
inherited_attributes.add(field.name)
# Concrete classes...
base = base._meta.concrete_model
base_key = make_model_tuple(base)
@ -246,6 +255,18 @@ class ModelBase(type):
auto_created=True,
parent_link=True,
)
if attr_name in field_names:
raise FieldError(
"Auto-generated field '%s' in class %r for "
"parent_link to base class %r clashes with "
"declared field of the same name." % (
attr_name,
name,
base.__name__,
)
)
# Only add the ptr field if it's not already present;
# e.g. migrations will already have it specified
if not hasattr(new_class, attr_name):
@ -256,16 +277,19 @@ class ModelBase(type):
else:
base_parents = base._meta.parents.copy()
# .. and abstract ones.
# Add fields from abstract base class if it wasn't overridden.
for field in parent_fields:
new_field = copy.deepcopy(field)
new_class.add_to_class(field.name, new_field)
# Replace parent links defined on this base by the new
# field as it will be appropriately resolved if required.
if field.one_to_one:
for parent, parent_link in base_parents.items():
if field == parent_link:
base_parents[parent] = new_field
if (field.name not in field_names and
field.name not in new_class.__dict__ and
field.name not in inherited_attributes):
new_field = copy.deepcopy(field)
new_class.add_to_class(field.name, new_field)
# Replace parent links defined on this base by the new
# field. It will be appropriately resolved if required.
if field.one_to_one:
for parent, parent_link in base_parents.items():
if field == parent_link:
base_parents[parent] = new_field
# Pass any non-abstract parent classes onto child.
new_class._meta.parents.update(base_parents)
@ -281,13 +305,18 @@ class ModelBase(type):
# Inherit private fields (like GenericForeignKey) from the parent
# class
for field in base._meta.private_fields:
if base._meta.abstract and field.name in field_names:
raise FieldError(
'Local field %r in class %r clashes '
'with field of similar name from '
'abstract base class %r' % (field.name, name, base.__name__)
)
new_class.add_to_class(field.name, copy.deepcopy(field))
if field.name in field_names:
if not base._meta.abstract:
raise FieldError(
'Local field %r in class %r clashes with field of '
'the same name from base class %r.' % (
field.name,
name,
base.__name__,
)
)
else:
new_class.add_to_class(field.name, copy.deepcopy(field))
if abstract:
# Abstract base models can't be instantiated and don't appear in

2
docs/releases/1.10.txt
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@ -400,6 +400,8 @@ Models
app label and class interpolation using the ``'%(app_label)s'`` and
``'%(class)s'`` strings.
* Allowed overriding model fields inherited from abstract base classes.
* The :func:`~django.db.models.prefetch_related_objects` function is now a
public API.

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

354
tests/model_inheritance/test_abstract_inheritance.py Normal file
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@ -0,0 +1,354 @@
from __future__ import unicode_literals
from django.contrib.contenttypes.fields import (
GenericForeignKey, GenericRelation,
)
from django.contrib.contenttypes.models import ContentType
from django.core.checks import Error
from django.core.exceptions import FieldDoesNotExist, FieldError
from django.db import models
from django.test import TestCase
from django.test.utils import isolate_apps
@isolate_apps('model_inheritance')
class AbstractInheritanceTests(TestCase):
def test_single_parent(self):
class AbstractBase(models.Model):
name = models.CharField(max_length=30)
class Meta:
abstract = True
class AbstractDescendant(AbstractBase):
name = models.CharField(max_length=50)
class Meta:
abstract = True
class DerivedChild(AbstractBase):
name = models.CharField(max_length=50)
class DerivedGrandChild(AbstractDescendant):
pass
self.assertEqual(AbstractDescendant._meta.get_field('name').max_length, 50)
self.assertEqual(DerivedChild._meta.get_field('name').max_length, 50)
self.assertEqual(DerivedGrandChild._meta.get_field('name').max_length, 50)
def test_multiple_parents_mro(self):
class AbstractBaseOne(models.Model):
class Meta:
abstract = True
class AbstractBaseTwo(models.Model):
name = models.CharField(max_length=30)
class Meta:
abstract = True
class DescendantOne(AbstractBaseOne, AbstractBaseTwo):
class Meta:
abstract = True
class DescendantTwo(AbstractBaseOne, AbstractBaseTwo):
name = models.CharField(max_length=50)
class Meta:
abstract = True
class Derived(DescendantOne, DescendantTwo):
pass
self.assertEqual(DescendantOne._meta.get_field('name').max_length, 30)
self.assertEqual(DescendantTwo._meta.get_field('name').max_length, 50)
self.assertEqual(Derived._meta.get_field('name').max_length, 50)
def test_multiple_inheritance_cannot_shadow_concrete_inherited_field(self):
class ConcreteParent(models.Model):
name = models.CharField(max_length=255)
class AbstractParent(models.Model):
name = models.IntegerField()
class Meta:
abstract = True
class FirstChild(ConcreteParent, AbstractParent):
pass
class AnotherChild(AbstractParent, ConcreteParent):
pass
self.assertIsInstance(FirstChild._meta.get_field('name'), models.CharField)
self.assertEqual(
AnotherChild.check(),
[Error(
"The field 'name' clashes with the field 'name' "
"from model 'model_inheritance.concreteparent'.",
obj=AnotherChild._meta.get_field('name'),
id="models.E006",
)]
)
def test_virtual_field(self):
class RelationModel(models.Model):
content_type = models.ForeignKey(ContentType, models.CASCADE)
object_id = models.PositiveIntegerField()
content_object = GenericForeignKey('content_type', 'object_id')
class RelatedModelAbstract(models.Model):
field = GenericRelation(RelationModel)
class Meta:
abstract = True
class ModelAbstract(models.Model):
field = models.CharField(max_length=100)
class Meta:
abstract = True
class OverrideRelatedModelAbstract(RelatedModelAbstract):
field = models.CharField(max_length=100)
class ExtendModelAbstract(ModelAbstract):
field = GenericRelation(RelationModel)
self.assertIsInstance(OverrideRelatedModelAbstract._meta.get_field('field'), models.CharField)
self.assertIsInstance(ExtendModelAbstract._meta.get_field('field'), GenericRelation)
def test_cannot_override_indirect_abstract_field(self):
class AbstractBase(models.Model):
name = models.CharField(max_length=30)
class Meta:
abstract = True
class ConcreteDescendant(AbstractBase):
pass
msg = (
"Local field 'name' in class 'Descendant' clashes with field of "
"the same name from base class 'ConcreteDescendant'."
)
with self.assertRaisesMessage(FieldError, msg):
class Descendant(ConcreteDescendant):
name = models.IntegerField()
def test_override_field_with_attr(self):
class AbstractBase(models.Model):
first_name = models.CharField(max_length=50)
last_name = models.CharField(max_length=50)
middle_name = models.CharField(max_length=30)
full_name = models.CharField(max_length=150)
class Meta:
abstract = True
class Descendant(AbstractBase):
middle_name = None
def full_name(self):
return self.first_name + self.last_name
with self.assertRaises(FieldDoesNotExist):
Descendant._meta.get_field('middle_name')
with self.assertRaises(FieldDoesNotExist):
Descendant._meta.get_field('full_name')
def test_overriding_field_removed_by_concrete_model(self):
class AbstractModel(models.Model):
foo = models.CharField(max_length=30)
class Meta:
abstract = True
class RemovedAbstractModelField(AbstractModel):
foo = None
class OverrideRemovedFieldByConcreteModel(RemovedAbstractModelField):
foo = models.CharField(max_length=50)
self.assertEqual(OverrideRemovedFieldByConcreteModel._meta.get_field('foo').max_length, 50)
def test_shadowed_fkey_id(self):
class Foo(models.Model):
pass
class AbstractBase(models.Model):
foo = models.ForeignKey(Foo, models.CASCADE)
class Meta:
abstract = True
class Descendant(AbstractBase):
foo_id = models.IntegerField()
self.assertEqual(
Descendant.check(),
[Error(
"The field 'foo_id' clashes with the field 'foo' "
"from model 'model_inheritance.descendant'.",
obj=Descendant._meta.get_field('foo_id'),
id='models.E006',
)]
)
def test_shadow_related_name_when_set_to_none(self):
class AbstractBase(models.Model):
bar = models.IntegerField()
class Meta:
abstract = True
class Foo(AbstractBase):
bar = None
foo = models.IntegerField()
class Bar(models.Model):
bar = models.ForeignKey(Foo, models.CASCADE, related_name='bar')
self.assertEqual(Bar.check(), [])
def test_reverse_foreign_key(self):
class AbstractBase(models.Model):
foo = models.CharField(max_length=100)
class Meta:
abstract = True
class Descendant(AbstractBase):
pass
class Foo(models.Model):
foo = models.ForeignKey(Descendant, models.CASCADE, related_name='foo')
self.assertEqual(
Foo._meta.get_field('foo').check(),
[
Error(
"Reverse accessor for 'Foo.foo' clashes with field name 'Descendant.foo'.",
hint=(
"Rename field 'Descendant.foo', or add/change a related_name "
"argument to the definition for field 'Foo.foo'."
),
obj=Foo._meta.get_field('foo'),
id='fields.E302',
),
Error(
"Reverse query name for 'Foo.foo' clashes with field name 'Descendant.foo'.",
hint=(
"Rename field 'Descendant.foo', or add/change a related_name "
"argument to the definition for field 'Foo.foo'."
),
obj=Foo._meta.get_field('foo'),
id='fields.E303',
),
]
)
def test_multi_inheritance_field_clashes(self):
class AbstractBase(models.Model):
name = models.CharField(max_length=30)
class Meta:
abstract = True
class ConcreteBase(AbstractBase):
pass
class AbstractDescendant(ConcreteBase):
class Meta:
abstract = True
class ConcreteDescendant(AbstractDescendant):
name = models.CharField(max_length=100)
self.assertEqual(
ConcreteDescendant.check(),
[Error(
"The field 'name' clashes with the field 'name' from "
"model 'model_inheritance.concretebase'.",
obj=ConcreteDescendant._meta.get_field('name'),
id="models.E006",
)]
)
def test_override_one2one_relation_auto_field_clashes(self):
class ConcreteParent(models.Model):
name = models.CharField(max_length=255)
class AbstractParent(models.Model):
name = models.IntegerField()
class Meta:
abstract = True
msg = (
"Auto-generated field 'concreteparent_ptr' in class 'Descendant' "
"for parent_link to base class 'ConcreteParent' clashes with "
"declared field of the same name."
)
with self.assertRaisesMessage(FieldError, msg):
class Descendant(ConcreteParent, AbstractParent):
concreteparent_ptr = models.CharField(max_length=30)
def test_abstract_model_with_regular_python_mixin_mro(self):
class AbstractModel(models.Model):
name = models.CharField(max_length=255)
age = models.IntegerField()
class Meta:
abstract = True
class Mixin(object):
age = None
class Mixin2(object):
age = 2
class DescendantMixin(Mixin):
pass
class ConcreteModel(models.Model):
foo = models.IntegerField()
class ConcreteModel2(ConcreteModel):
age = models.SmallIntegerField()
def fields(model):
if not hasattr(model, '_meta'):
return list()
return list((f.name, f.__class__) for f in model._meta.get_fields())
model_dict = {'__module__': 'model_inheritance'}
model1 = type(str('Model1'), (AbstractModel, Mixin), model_dict.copy())
model2 = type(str('Model2'), (Mixin2, AbstractModel), model_dict.copy())
model3 = type(str('Model3'), (DescendantMixin, AbstractModel), model_dict.copy())
model4 = type(str('Model4'), (Mixin2, Mixin, AbstractModel), model_dict.copy())
model5 = type(str('Model5'), (Mixin2, ConcreteModel2, Mixin, AbstractModel), model_dict.copy())
self.assertEqual(
fields(model1),
[('id', models.AutoField), ('name', models.CharField), ('age', models.IntegerField)]
)
self.assertEqual(fields(model2), [('id', models.AutoField), ('name', models.CharField)])
self.assertEqual(getattr(model2, 'age'), 2)
self.assertEqual(fields(model3), [('id', models.AutoField), ('name', models.CharField)])
self.assertEqual(fields(model4), [('id', models.AutoField), ('name', models.CharField)])
self.assertEqual(getattr(model4, 'age'), 2)
self.assertEqual(
fields(model5),
[
('id', models.AutoField), ('foo', models.IntegerField),
('concretemodel_ptr', models.OneToOneField),
('age', models.SmallIntegerField), ('concretemodel2_ptr', models.OneToOneField),
('name', models.CharField),
]
)