#34555: ModelBase metaclass implementation prevents addition of model fields via
__init_subclass__
-------------------------------------+-------------------------------------
Reporter: hottwaj | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 4.2
(models, ORM) |
Severity: Normal | Resolution: wontfix
Keywords: ModelBase | Triage Stage:
init_subclass | Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Clifford Gama):
Replying to [comment:10 Carlton Gibson]:
> Related too is #27880 ''Use `__set_name__` to replace some usages of
contribute_to_class'', I think
Indeed, if #27880 gets added then this might be fixed, thanks to
`Options.__set_name__()`, `_meta` will be added when the class is first
created.
I say *might* because as the PR for #27880 currently stands,
`Field.contribute_to_class()` will still be called after the class is
first created, because `Field.contribute_to_class()` is semi-private API
and has to be deprecated rather than replaced.
Regardless of whether `Field.contribute_to_class()` is deprecated for
`Field.__set_name__()`, if
[https://github.com/django/django/pull/18621/commits/f5fa7b4986e0ef2c994dffc95c003f55bf7dbe8c
f5fa7b4] is added allowing Options to be added on class creation (i.e.
`type.__new__()` in `ModelBase`) then the following would work
{{{#!python
from django.db.models import Model, ForeignKey, CASCADE, CharField
class BaseBookModel(Model):
class Meta:
abstract = True
def __init_subclass__(cls, author_model_cls: Type[Model], **kwargs,):
super().__init_subclass__(**kwargs)
author = ForeignKey(author_model_cls, on_delete = CASCADE)
# This will work because `_meta` is available when init-subclass
is called
author.contribute_to_class(cls, 'author')
# author.__set_name__(cls, 'author') if #27880 is landed for
Fields
class Author(Model):
name = CharField(max_len = 256, unique = True)
class Book(BaseBookModel, author_model_cls = Author):
pass
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/34555#comment:12>
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