Related model 'company.user' cannot be resolved

[Mike Dewhirst]

I moved my custom user and userprofile models from my 'common' app into
my 'company' app by way of locking the model tables first (db_table =
"common_user" and so on) and just plain refactoring.

That has all worked sort of as expected in that Company and User models
now appear in the company app space in the Admin which was my original
motivation.

makemigrations wanted to destroy data with delete/create models in order
to move them and of course I couldn't let that happen. migrate --fake
and migrate --fake-initial wouldn't work due to lots of other models
looking for settings.AUTH_USER_MODEL which Django couldn't find in the
company app so I finessed my own fake migrations. That also seemed to
work and the job seemed done.

BUT manage.py test now fails with "Related model 'company.user' cannot
be resolved"

StackOverflow seems to indicate my finessed migrations are at fault. I
have tried to tweak the dependencies with no luck as follows ...

# company.migrations.0005_user_userprofile.py
...
    dependencies = [
        ('auth', '0012_alter_user_first_name_max_length'),
        ('company', '0004_auto_20210510_1431'),       # older pre move
migration
        ('common', '0008_auto_20210705_1740'),        # see below
    ]

    operations = [
        migrations.CreateModel(
            name='User',
            fields=[
                ('id', models.BigAutoField(auto_created=True,
primary_key=True, serialize=False, verbose_name='ID')),
                ('password', models.CharField(max_length=128,
verbose_name='password')),
... etc for creating both User and UserProfile models

# common.migrations.0008_auto_20210705_1740.py
...
    dependencies = [
        ('common', '0007_userprofile_job_title'),    # older pre-move
migration
    ]

    operations = [
        migrations.RemoveField(
            model_name='userprofile',
            name='company',
        ),
        migrations.RemoveField(
            model_name='userprofile',
            name='user',
        ),
        migrations.DeleteModel(
            name='User',
        ),
        migrations.DeleteModel(
            name='UserProfile',
        ),
    ]


Django 3.2.5, Python 3.8

I feel I should have zigged when I should've zagged. Thanks for any
suggestions

Mike

Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\__init__.py",
line 419, in execute_from_command_line
    utility.execute()
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\__init__.py",
line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\commands\test.py",
line 23, in run_from_argv
    super().run_from_argv(argv)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\base.py",
line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\base.py",
line 398, in execute
    output = self.handle(*args, **options)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\commands\test.py",
line 55, in handle
    failures = test_runner.run_tests(test_labels)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\test\runner.py", line
725, in run_tests
    old_config = self.setup_databases(aliases=databases)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\test\runner.py", line
643, in setup_databases
    return _setup_databases(
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\test\utils.py", line
179, in setup_databases
    connection.creation.create_test_db(
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\backends\base\creation.py",
line 74, in create_test_db
    call_command(
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\__init__.py",
line 181, in call_command
    return command.execute(*args, **defaults)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\base.py",
line 398, in execute
    output = self.handle(*args, **options)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\base.py",
line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\core\management\commands\migrate.py",
line 244, in handle
    post_migrate_state = executor.migrate(
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\migrations\executor.py",
line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan,
fake=fake, fake_initial=fake_initial)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\migrations\executor.py",
line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake,
fake_initial=fake_initial)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\migrations\executor.py",
line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\migrations\migration.py",
line 126, in apply
    operation.database_forwards(self.app_label, schema_editor,
old_state, project_state)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\migrations\operations\models.py",
line 92, in database_forwards
    schema_editor.create_model(model)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\backends\base\schema.py",
line 343, in create_model
    sql, params = self.table_sql(model)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\backends\base\schema.py",
line 162, in table_sql
    definition, extra_params = self.column_sql(model, field)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\backends\base\schema.py",
line 215, in column_sql
    db_params = field.db_parameters(connection=self.connection)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 1004, in db_parameters
    return {"type": self.db_type(connection), "check":
self.db_check(connection)}
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 1001, in db_type
    return self.target_field.rel_db_type(connection=connection)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 897, in target_field
    return self.foreign_related_fields[0]
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\utils\functional.py",
line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 644, in foreign_related_fields
    return tuple(rhs_field for lhs_field, rhs_field in
self.related_fields if rhs_field)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\utils\functional.py",
line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 632, in related_fields
    return self.resolve_related_fields()
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 936, in resolve_related_fields
    related_fields = super().resolve_related_fields()
  File
"D:\Users\mike\envs\xxai\lib\site-packages\django\db\models\fields\related.py",
line 615, in resolve_related_fields
    raise ValueError('Related model %r cannot be resolved' %
self.remote_field.model)
ValueError: Related model 'company.user' cannot be resolved


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[Mike Dewhirst]

It seems I have to meddle with history and persuade the testing harness
that my custom user model has been in the company app from the beginning
of time. See story below.

Upside is that testing will (might) start working again. Downside is
I'll go mad.

Any ideas?

Thanks

Mike

[Mike Dewhirst]

On 7/07/2021 9:56 am, Mike Dewhirst wrote:
> It seems I have to meddle with history and persuade the testing
> harness that my custom user model has been in the company app from the
> beginning of time. See story below.
>
> Upside is that testing will (might) start working again. Downside is
> I'll go mad.

All upside!

So in summary ...

0. The mission was to move all models (User and UserProfile) from the
common app to the company app so users and companies would both appear
in the Admin in the same app. This simplifies the site adminstration
main menu for new users.

1. In class Meta: in both models User/UserProfile, add db_table =
common_user/userprofile[1]. This will have no effect and should be
committed, migrated and deployed to production.

2. Branch the code and switch to create an escape route.

3. Relocate User and UserProfile models from app common to app company[2]

4. Refactor entire codebase using company_ instead of common_ [3]

5. makemigrations[4] but do not migrate to avoid deleting tables.

Now the tricky bit. What I did was probably wrong and any expert is
welcome to suggest an improvement but because of steps 1 and 2 there was
always a retreat. The mission here is to tweak the migrations so the
test harness can create a test database without error.

6. Delete the migration which deletes User and UserProfile tables from
common

7. Edit company/migrations/0001_initial.py to include the contents of
the latest migration which created User and UserProfile in company so
that the test harness thinks they have been there since the beginning.
Then delete that latest company migration too.

8. Delete all migrations in common/migrations including __pycache__ [5]

9. Cross fingers and run your tests. Resolve any errors by adjusting
dependencies which includes positioning User and UserProfile higher or
lower in 0001_initial.py in company/migrations[6].

10. Consider editing your django_migrations table to remove rows
relating to deleted migrations. This is for future-proofing in case you
ever decide to put any tables back in the common app. If 0001_initial is
mentioned in that table it will be a confusing preventer.

11. Merge your successful changes back to your main branch and deploy.


[1] One day I will rename the tables so everything lines up but for now
that is a step too far

[2] I did try leaving the models in place and importing them into the
company app but things quickly got messy. Much easier to bite the bullet
and just physically move the files.

[3] At this point the software should work but unit testing will fail
because the test database is always generated from the sum total of all
migrations

[4] This will make table deletions from common and table creations in
company BUT the creations will be for the current state. This becomes
significant later in the process.

[5] All migrations in common/migrations were for the only two models in
the common app. Because the creation migration was for the current
state, none of the other migrations were needed. However, your mileage
may vary perhaps if your migrations did other things than just changing
structure etc. If you also did some data tweaking in some migrations you
will want to think a bit harder before deleting them.

[6] In my case I needed to put User at the beginning and UserProfile at
the end of that migration. Here is the relevant piece of my
company/migrations/0001_initial.py  ... note the db_table in options ...



class Migration(migrations.Migration):

initial = True

dependencies = [
('auth', '0012_alter_user_first_name_max_length'),

migrations.swappable_dependency(settings.AUTH_USER_MODEL),

]

operations = [
migrations.CreateModel(
name='User',
fields=[
('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
('password', models.CharField(max_length=128, verbose_name='password')),

('last_login', models.DateTimeField(blank=True, null=True, verbose_name='last login')),
('is_superuser', models.BooleanField(default=False, help_text='Designates that this user has all permissions without explicitly assigning them.', verbose_name='superuser status')),
('username', models.CharField(error_messages={'unique': 'A user with that username already exists.'}, help_text='Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.', max_length=150, unique=True, validators=[django.contrib.auth.validators.UnicodeUsernameValidator()], verbose_name='username')),
('date_joined', models.DateTimeField(default=django.utils.timezone.now, verbose_name='date joined')),
('first_name', models.CharField(blank=True, max_length=30, verbose_name='short name')),
('last_name', models.CharField(blank=True, max_length=150, verbose_name='full name')),
('email', models.EmailField(blank=True, help_text='This is the address used for a forgotten password reset token', max_length=254, verbose_name='email address')),
('is_staff', models.BooleanField(default=True, help_text='Designates whether the user can log into this admin site', verbose_name='staff status')),
('is_active', models.BooleanField(default=True, help_text='Designates if this account is usable. Uncheck for users away on leave.', verbose_name='active')),
('groups', models.ManyToManyField(blank=True, help_text='The groups this user belongs to. A user will get all permissions granted to each of their groups.', related_name='user_set', related_query_name='user', to='auth.Group', verbose_name='groups')),
('user_permissions', models.ManyToManyField(blank=True, help_text='Specific permissions for this user.', related_name='user_set', related_query_name='user', to='auth.Permission', verbose_name='user permissions')),
],
options={
'verbose_name': 'user',
'verbose_name_plural': 'users',
'db_table': 'common_user',
'abstract': False,
'swappable': 'AUTH_USER_MODEL',
},
managers=[
('objects', company.models.user.CaseInsensitiveUserManager()),
],
),

... inital company migrations which are untouched ...

migrations.CreateModel(
name='UserProfile',

fields=[
('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),

('job_title', models.CharField(blank=True, default='', help_text="Only required for users in the 'manager' role. Used for AICIS annual declarations.", max_length=128, null=True, verbose_name='Job title')),
('cellphone', models.CharField(blank=True, default='', help_text='In the form +61 (0)411 704 143. A valid phone number is required here if this user needs admin permissions.', max_length=32, null=True, verbose_name='Mobile or cellphone')),
('region', models.CharField(blank=True, choices=[('au', 'Australia'), ('ca', 'Canada'), ('cn', 'China'), ('de', 'Germany'), ('es', 'Spain'), ('fr', 'France'), ('ie', 'Ireland'), ('in', 'India'), ('it', 'Italy'), ('jp', 'Japan'), ('nl', 'The Netherlands'), ('nz', 'New Zealand'), ('uk', 'United Kingdom'), ('us', 'United States')], default='au', help_text='Used for selecting currency and GST/VAT rules if necessary.', max_length=2)),
('created', models.DateTimeField(auto_now_add=True)),
('modified', models.DateTimeField(auto_now=True)),
('company', models.ForeignKey(blank=True, help_text='Each user may only be associated with <strong>one</strong> company', null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='usercompany', to='company.company')),
('user', models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, related_name='userprofile', to=settings.AUTH_USER_MODEL)),
],
options={
'verbose_name': 'user profile',
'verbose_name_plural': 'user profile',
'db_table': 'common_userprofile',
},
),
]

Cheers

Mike