#30254: Custom model metaclasses cannot access the attribute dict in __init__
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Reporter: Matt | Owner: nobody
Westcott |
Type: Bug | Status: new
Component: Database | Version: 2.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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In Django <=2.2, it is possible for models to define a custom metaclass
(as a subclass of `models.base.ModelBase`) and access the attribute dict
of the class being defined:
{{{
from django.db import models
class PageBase(models.base.ModelBase):
def __init__(cls, name, bases, dct):
super(PageBase, cls).__init__(name, bases, dct)
if 'magic' in dct:
print("enabling magic on %s" % (name))
class Page(models.Model, metaclass=PageBase):
magic = True
title = models.CharField(max_length=255)
}}}
As of commit a68ea231012434b522ce45c513d84add516afa60, this fails because
all attributes without a `contribute_to_class` method are popped from the
dict in `ModelBase.__new__` .
(This pattern is used by Wagtail's Page model
https://github.com/wagtail/wagtail/blob/3e1e67021e0a20783ed59e17b43e3c481897fce3/wagtail/core/models.py#L190
, so this is causing various failures against django stable/2.2.x.)
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Ticket URL: <https://code.djangoproject.com/ticket/30254>
Django <https://code.djangoproject.com/>
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