#33234: Migrations autodetector breaking with proxy models inheriting from mixin
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Reporter: Kevin Marsh | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 4.0
Severity: Normal | Keywords: proxy model
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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So I've run into an issue with the new automigrations feature in Django
4.0b1 (and 4.0a1) relating to proxy models inheriting from a non-Model
class.
For examples given these three models:
{{{#!python
from django.db import models
class MyMixin:
...
class MyRealModel(MyMixin, models.Model):
...
class MyBaseModel(models.Model):
...
class MyProxyModel(MyMixin, MyBaseModel):
class Meta:
proxy = True
}}}
Running `migrate`/`makemigrations` will result in `MyProxyModel` crashing
when it tries running `_find_concrete_model_from_proxy`:
{{{
File
"/some/annonymized/path/django/core/management/commands/makemigrations.py",
line 172, in handle
changes = autodetector.changes(
File "/some/annonymized/path/django/db/migrations/autodetector.py", line
43, in changes
changes = self._detect_changes(convert_apps, graph)
File "/some/annonymized/path/django/db/migrations/autodetector.py", line
156, in _detect_changes
self.to_state.resolve_fields_and_relations()
File "/some/annonymized/path/django/db/migrations/state.py", line 449,
in resolve_fields_and_relations
concretes, proxies =
self._get_concrete_models_mapping_and_proxy_models()
File "/some/annonymized/path/django/db/migrations/state.py", line 470,
in _get_concrete_models_mapping_and_proxy_models
concrete_models_mapping[model_key] =
self._find_concrete_model_from_proxy(
File "/some/annonymized/path/django/db/migrations/state.py", line 479,
in _find_concrete_model_from_proxy
base_key = make_model_tuple(base)
File "/some/annonymized/path/django/db/models/utils.py", line 18, in
make_model_tuple
model_tuple = model._meta.app_label, model._meta.model_name
AttributeError: type object 'MyMixin' has no attribute '_meta'
}}}
Changing `MyMixin` to inherit from `models.Model` prevents this crash but
might not always be possible depending on how the user is using that
mixin. Or if we've decided that all inheritance for proxy models must be
from `models.Model` then that should be flagged up more explicitly to
developers (eg. checking for it in `ModelBase.__new__` or something).
--
Ticket URL: <https://code.djangoproject.com/ticket/33234>
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