id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
29897	Initial migration fails when referencing a custom user model from a sequence of at least two concrete ancestor models	Steven Ganz	nobody	"The following model fails on initial migration.
{{{
from django.db import models
from django.contrib.auth.models import (AbstractBaseUser)

class A(models.Model):
    createdByUser = models.ForeignKey('User', related_name='creations+', verbose_name='creatorUser', blank=True, null=True, editable=False, on_delete=models.PROTECT)

class B(A):
    pass

class User(AbstractBaseUser, B):
    email = models.EmailField('email address', max_length=256, unique=True, db_index=True)
    USERNAME_FIELD = 'email'

    @property
    def username(self):
         return self.email
}}}

settings.py contains:
{{{
AUTH_USER_MODEL = 'core.User'
}}}

Output of running the migrations:
{{{
  Applying core.0001_initial...Traceback (most recent call last):
  File ""./manage.py"", line 13, in <module>
    execute_from_command_line(sys.argv)
  File "".../lib/python3.6/site-packages/django/core/management/__init__.py"", line 364, in execute_from_command_line
    utility.execute()
  File "".../lib/python3.6/site-packages/django/core/management/__init__.py"", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "".../lib/python3.6/site-packages/django/core/management/base.py"", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "".../lib/python3.6/site-packages/django/core/management/base.py"", line 330, in execute
    output = self.handle(*args, **options)
  File "".../lib/python3.6/site-packages/django/core/management/commands/migrate.py"", line 204, in handle
    fake_initial=fake_initial,
  File "".../lib/python3.6/site-packages/django/db/migrations/executor.py"", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "".../lib/python3.6/site-packages/django/db/migrations/executor.py"", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "".../lib/python3.6/site-packages/django/db/migrations/executor.py"", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "".../lib/python3.6/site-packages/django/db/migrations/migration.py"", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "".../lib/python3.6/site-packages/django/db/migrations/operations/fields.py"", line 88, in database_forwards
    field,
  File "".../lib/python3.6/site-packages/django/db/backends/base/schema.py"", line 431, in add_field
    definition, params = self.column_sql(model, field, include_default=True)
  File "".../lib/python3.6/site-packages/django/db/backends/base/schema.py"", line 160, in column_sql
    db_params = field.db_parameters(connection=self.connection)
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 994, in db_parameters
    return {""type"": self.db_type(connection), ""check"": self.db_check(connection)}
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 991, in db_type
    return self.target_field.rel_db_type(connection=connection)
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 909, in target_field
    return self.foreign_related_fields[0]
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 653, in foreign_related_fields
    return tuple(rhs_field for lhs_field, rhs_field in self.related_fields if rhs_field)
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 640, in related_fields
    self._related_fields = self.resolve_related_fields()
  File "".../lib/python3.6/site-packages/django/db/models/fields/related.py"", line 625, in resolve_related_fields
    raise ValueError('Related model %r cannot be resolved' % self.remote_field.model)
ValueError: Related model 'core.User' cannot be resolved
}}}

Notably, this works fine with any of the following modifications:
- model B is removed, closing the chain
- createdByUser is moved to B or removed altogether
- either A or B is made abstract
- the referenced model is not the custom user model

This is not just a matter of preference for concrete classes, as only a concrete class can be referenced through a foreign key."	Bug	closed	Migrations	2.1	Normal	fixed	"""custom user model"" ""abstract model"" ""foreign key"""		Accepted	1	0	0	0	0	0