'self'-referencing relationship causes crash

[jacobjove]

Traceback

Traceback (most recent call last):
  File "mypy/checkexpr.py", line 3898, in accept
  File "mypy/nodes.py", line 1555, in accept
  File "mypy/checkexpr.py", line 270, in visit_call_expr
  File "mypy/checkexpr.py", line 347, in visit_call_expr_inner
  File "mypy/checkexpr.py", line 852, in check_call_expr_with_callee_type
  File "mypy/checkexpr.py", line 911, in check_call
  File "mypy/checkexpr.py", line 1023, in check_callable_call
  File "mypy/checkexpr.py", line 732, in apply_function_plugin
  File "/Users/jacob/modularhistory/.venv/lib/python3.9/site-packages/mypy_django_plugin/transformers/orm_lookups.py", line 31, in typecheck_queryset_filter
    lookup_type = django_context.resolve_lookup_expected_type(ctx, model_cls, lookup_kwarg)
  File "/Users/jacob/modularhistory/.venv/lib/python3.9/site-packages/mypy_django_plugin/django/context.py", line 335, in resolve_lookup_expected_type
    lookup_parts, field_parts, is_expression = query.solve_lookup_type(lookup)
  File "/Users/jacob/modularhistory/.venv/lib/python3.9/site-packages/django/db/models/sql/query.py", line 1052, in solve_lookup_type
    _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
  File "/Users/jacob/modularhistory/.venv/lib/python3.9/site-packages/django/db/models/sql/query.py", line 1484, in names_to_path
    pathinfos = field.get_path_info(filtered_relation)
  File "/Users/jacob/modularhistory/.venv/lib/python3.9/site-packages/django/db/models/fields/related.py", line 723, in get_path_info
    opts = self.remote_field.model._meta
AttributeError: 'str' object has no attribute '_meta'
apps/trees/models.py:89: : note: use --pdb to drop into pdb

I did some debugging and found that when this 'str' object has no attribute '_meta' error happens, the value of self.remote_field is 'self'.

To Reproduce

Here's the abridged content of my models.py:

"""Based on https://github.com/peopledoc/django-ltree-demo."""

from typing import Type

from django.core.exceptions import ValidationError
from django.db.models.query import QuerySet
from django.utils.translation import ugettext_lazy as _

from core.models.model import Model


class TreeModel(Model):
    """Implements Postgres ltree for self-referencing hierarchy."""

    parent = models.ForeignKey(
        to='self',
        null=True,
        blank=True,
        related_name='children',
        on_delete=models.CASCADE,
        verbose_name=_('parent'),
    )
    name = models.TextField(verbose_name=_('name'))

    # https://docs.djangoproject.com/en/dev/ref/models/options/#model-meta-options
    class Meta:
        abstract = True

    @property
    def siblings(self) -> QuerySet['TreeModel']:
        """Return the model instances's siblings."""
        # Here is where it fails:
        return self.__class__.objects.exclude(id=self.id).filter(parent_id=self.parent_id)

[sobolevn]

Yes, looks like we need a special case for it. @iacobfred are you interested in working on this?

[jacobjove]

I'd be willing to give it a shot. I'm only a de facto developer, though, so it's possible that the typeddjango maintainers might be more pleased with someone else's efforts. ; )

[Kircheneer]

I am running into the same problem - I tried reproducing this in the test framework but couldn't get the error there. Can you give me a hint as to what is wrong with this test case? It just passes fine without an error.

-   case: test_self_referencing
    main: |
        from myapp.models import TreeModel
    installed_apps:
        -   myapp
    files:
        -   path: myapp/__init__.py
        -   path: myapp/models.py
            content: |
                from typing import Type

                from django.db import models
                from django.core.exceptions import ValidationError
                from django.db.models.query import QuerySet


                class TreeModel(models.Model):
                    parent = models.ForeignKey(
                        to='self',
                        null=True,
                        blank=True,
                        related_name='children',
                        on_delete=models.CASCADE,
                    )
                    name = models.TextField()

                    class Meta:
                        abstract = True

                    @property
                    def siblings(self) -> QuerySet['TreeModel']:
                        return self.__class__.objects.exclude(pk=self.pk).filter(parent=self.parent)