AttributeError: 'NoneType' object has no attribute '__module__' while referencing model as string in ForeignKey

[linevych]

Bug report

In the project that I'm working on I have an application with the following structure:

app1
└── models
    ├── bar.py
    ├── baz.py
    └── foo.py

There is a model ModelA defined in bar.py and ModelB defined in foo.py that has FK to ModelA:

class ModelB(models.Model):
    field1 = models.ForeignKey('ModelA')

This is a valid syntax for referencing model in the same application but when I run mypy I get an error.

What's wrong

Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
  File "/usr/local/lib/python3.6/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/usr/local/lib/python3.6/site-packages/mypy/main.py", line 83, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 164, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 224, in _build
    graph = dispatch(sources, manager, stdout)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2526, in dispatch
    graph = load_graph(sources, manager)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2748, in load_graph
    caller_state=st, caller_line=st.dep_line_map.get(dep, 1))
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 1772, in __init__
    self.compute_dependencies()
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2059, in compute_dependencies
    self.manager.plugin.get_additional_deps(self.tree))
  File "/usr/local/lib/python3.6/site-packages/mypy/plugin.py", line 743, in get_additional_deps
    deps.extend(plugin.get_additional_deps(file))
  File "/usr/local/lib/python3.6/site-packages/mypy_django_plugin/main.py", line 152, in get_additional_deps
    related_model_module = related_model_cls.__module__
AttributeError: 'NoneType' object has no attribute '__module__'

The problem is that mypy_django_plugin.django.context.DjangoContext.get_model_class_by_fullname in mypy_django_plugin.django.context.DjangoFieldsContext.get_related_model_cls returns None for relative reference in this case.

The only solution that I found is to use absolute reference models.ForeignKey('app1.ModelA') instead.

How is that should be

Relative model reference should be supported even in case if models.py is replaced with a module.

System information

• OS: Docker container based on python:3.6-alpine
• python version: 3.6.6
• django version: 2.2.5
• mypy version: 0.720
• django-stubs version: 1.1.0

[mkurnikov]

Sure it's valid? I thought that for Django to be able to find models, they all has to be reimported in the models/__init__.py file.
https://docs.djangoproject.com/en/2.2/topics/db/models/#organizing-models-in-a-package

UPD. I've reproduced a crash though, thanks!

[armanckeser]

I am getting the same error on mypy=1.4.1 and django-stubs=4.2.3

Output:
Traceback (most recent call last):
  File "/Users/ahmetkeser/Library/Caches/pypoetry/virtualenvs/venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/ahmetkeser/Library/Caches/pypoetry/virtualenvs/venv/lib/python3.9/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "mypy/main.py", line 95, in main
  File "mypy/main.py", line 174, in run_build
  File "mypy/build.py", line 197, in build
  File "mypy/build.py", line 270, in _build
  File "mypy/build.py", line 2874, in dispatch
  File "mypy/build.py", line 3060, in load_graph
  File "mypy/build.py", line 2001, in __init__
  File "mypy/build.py", line 2293, in compute_dependencies
  File "mypy/plugin.py", line 839, in get_additional_deps
  File "/Users/ahmetkeser/Library/Caches/pypoetry/virtualenvs/venv/lib/python3.9/site-packages/mypy_django_plugin/main.py", line 163, in get_additional_deps
    related_model_module = related_model_cls.__module__
AttributeError: 'NoneType' object has no attribute '__module__'

Downgrading makes it work again.
Package operations: 0 installs, 3 updates, 0 removals

• Updating mypy (1.4.1 -> 1.3.0)
• Updating django-stubs (4.2.3 -> 4.2.1)

I should say that the error is the same but might not be because of using a string in ForeignKey since my project does not do that.