Using m2m_fields in inheritated models

[bacheric]

Problem Statement
Access many-to-many fields of base model when using inheritance

Describe the solution you'd like
I have a question about using django-simple-history with models that support inheritation.

Basic example:

class Application(PolymorphicModel):
     users = ManyToManyField("User")

class SpecialApplication(Application):
     history=HistoricalRecords(m2m_fields=["users"]

This results in AttributeError: 'str' object has no attribute 'name'

I also tried using m2m_fields=[Application.users] but received AttributeError: 'ManyToManyDescriptor' object has no attribute 'name'.

How can I solve this?

Additional context

Edit: I am using Django Polymorphic for my base model, I don't know if this makes a difference, but I put it in the example.

The documentation says:

You may also define these fields in a model attribute (by default on _history_m2m_fields). This is mainly used for inherited models. You can override the attribute name by setting your own m2m_fields_model_field_name argument on the HistoricalRecord instance.

But I have no real clue how to use this. Is there an example somewhere?

[legau]

Hi, I made a PR(#1243) to allow declaring these fields by their name.

While waiting for the new release you can subclass HistoricalRecords with my changes.

[bacheric]

Hey @legau , many thanks for your response. However, I have trouble getting it to work. I created a very basic django project to make sure it is not an issue coming from my current code project. This file holds my models:

from django.conf import settings
from django.db import models
from polymorphic.models import PolymorphicModel

from mysite.polls.models.historical_records2 import HistoricalRecords2

class Application(PolymorphicModel):
     responsible = models.ManyToManyField(settings.AUTH_USER_MODEL,blank=True)
     
class SpecialApplication(Application):
    information = models.CharField(max_length=100)
    history = HistoricalRecords2(m2m_fields=["responsible"])
    

HistoricalRecords 2:

from simple_history.models import HistoricalRecords


class HistoricalRecords2(HistoricalRecords):
    def get_m2m_fields_from_model(self, model):
        m2m_fields = set(self.m2m_fields)
        try:
            m2m_fields.update(getattr(model, self.m2m_fields_model_field_name))
        except AttributeError:
            pass
        field_names = [
            field if isinstance(field, str) else field.name for field in m2m_fields
        ]
        return [getattr(model, field_name).field for field_name in field_names]

Now, whenever I try to save a SpecialApplication instance (inside django admin for example), I receive an error with the following stacktrace:

Environment:


Request Method: POST
Request URL: http://localhost:8000/admin/polls/specialapplication/add/

Django Version: 4.2.5
Python Version: 3.11.1
Installed Applications:
['mysite.polls',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'polymorphic',
 'simple_history']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'simple_history.middleware.HistoryRequestMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/options.py", line 688, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/utils/decorators.py", line 134, in _wrapper_view
    response = view_func(request, *args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/views/decorators/cache.py", line 62, in _wrapper_view_func
    response = view_func(request, *args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/sites.py", line 242, in inner
    return view(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/options.py", line 1886, in add_view
    return self.changeform_view(request, None, form_url, extra_context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/utils/decorators.py", line 46, in _wrapper
    return bound_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/utils/decorators.py", line 134, in _wrapper_view
    response = view_func(request, *args, **kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/options.py", line 1747, in changeform_view
    return self._changeform_view(request, object_id, form_url, extra_context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/options.py", line 1798, in _changeform_view
    self.save_model(request, new_object, form, not add)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/contrib/admin/options.py", line 1227, in save_model
    obj.save()
    ^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/polymorphic/models.py", line 87, in save
    return super().save(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/base.py", line 814, in save
    self.save_base(
    ^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/base.py", line 892, in save_base
    post_save.send(
    ^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/dispatch/dispatcher.py", line 176, in send
    return [
           
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/dispatch/dispatcher.py", line 177, in <listcomp>
    (receiver, receiver(signal=self, sender=sender, **named))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/simple_history/models.py", line 637, in post_save
    self.create_historical_record(instance, created and "+" or "~", using=using)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/simple_history/models.py", line 736, in create_historical_record
    self.create_historical_record_m2ms(history_instance, instance)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/simple_history/models.py", line 673, in create_historical_record_m2ms
    rows = through_model.objects.filter(**{through_field_name: instance})
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/manager.py", line 87, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/query.py", line 1436, in filter
    return self._filter_or_exclude(False, args, kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/query.py", line 1454, in _filter_or_exclude
    clone._filter_or_exclude_inplace(negate, args, kwargs)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/query.py", line 1461, in _filter_or_exclude_inplace
    self._query.add_q(Q(*args, **kwargs))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/sql/query.py", line 1545, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/sql/query.py", line 1576, in _add_q
    child_clause, needed_inner = self.build_filter(
                                 
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/sql/query.py", line 1426, in build_filter
    lookups, parts, reffed_expression = self.solve_lookup_type(arg, summarize)
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/sql/query.py", line 1236, in solve_lookup_type
    _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/eric/repos/m2mtest/venv/lib/python3.11/site-packages/django/db/models/sql/query.py", line 1724, in names_to_path
    raise FieldError(
    ^

Exception Type: FieldError at /admin/polls/specialapplication/add/
Exception Value: Cannot resolve keyword 'specialapplication' into field. Choices are: application, application_id, id, user, user_id

I attached the sample project to this comment. I would be very grateful if you could take a look at it to see whats wrong. :)

mysite.zip

[legau]

After some tries against dsh master branch it looks like you also need #1218 which was merged 2 weeks ago

[bacheric]

Many thanks, after adding the changes of both #1218 and #1243 it works as expected!