python - Django relation error when running make migrations

Question

Hey I am attempting to initialize a new database, but I am running into some issues setting up the migrations. The error I am getting appears to stem from setting up my forms. In a form I am using, I am creating a choice field as so:

from django import forms
from ..custom_admin import widgets, choices


class MemberForm(forms.Form):
    provinces = forms.ChoiceField(label='Provinces', choices=choices.PROVINCE_CHOICES, required=True)

where PROVINCE_CHOICES comes from here:

from ..base.models import ProvinceCode

PROVINCE_CHOICES = []
for province in ProvinceCode.objects.filter(country_code_id=1).order_by('code'):
    PROVINCE_CHOICES.append((province.code, province.code))

The issue seems to be that this loop is being called before the migrations occur, giving me an error stating that the Province model does not exist. Commenting out the reference to this file allows the migrations to work, however, that seems like an impractical solution for continued use. Is there a way to get around this error?

For reference, here is the error I get when I run manage.py makemigrations:

./manage.py makemigrations        
Traceback (most recent call last):
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: relation "pc_psr_code" does not exist
LINE 1: ...escription", "pc_psr_code"."country_code_id" FROM "pc_psr_co...
                                                             ^


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "./manage.py", line 9, in <module>
    django.setup()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/apps/registry.py", line 115, in populate
    app_config.ready()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/debug_toolbar/apps.py", line 15, in ready
    dt_settings.patch_all()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/debug_toolbar/settings.py", line 228, in patch_all
    patch_root_urlconf()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/debug_toolbar/settings.py", line 216, in patch_root_urlconf
    reverse('djdt:render_panel')
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/core/urlresolvers.py", line 568, in reverse
    app_list = resolver.app_dict[ns]
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/core/urlresolvers.py", line 360, in app_dict
    self._populate()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/core/urlresolvers.py", line 293, in _populate
    for pattern in reversed(self.url_patterns):
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/utils/functional.py", line 33, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/core/urlresolvers.py", line 417, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/utils/functional.py", line 33, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/core/urlresolvers.py", line 410, in urlconf_module
    return import_module(self.urlconf_name)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 986, in _gcd_import
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 662, in exec_module
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "/Users/js/Documents/app/platform/test/pc/urls.py", line 7, in <module>
    from .custom_admin import urls as custom_urls
  File "/Users/js/Documents/app/platform/test/pc/custom_admin/urls.py", line 3, in <module>
    from ..party import views as party_views
  File "/Users/js/Documents/app/platform/test/pc/party/views.py", line 1, in <module>
    from ..party import forms
  File "/Users/js/Documents/app/platform/test/pc/party/forms.py", line 2, in <module>
    from ..custom_admin import widgets, choices
  File "/Users/js/Documents/app/platform/test/pc/custom_admin/choices.py", line 9, in <module>
    for province in ProvinceCode.objects.filter(country_code_id=1).order_by('code'):
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/models/query.py", line 258, in __iter__
    self._fetch_all()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/models/query.py", line 1074, in _fetch_all
    self._result_cache = list(self.iterator())
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/models/query.py", line 52, in __iter__
    results = compiler.execute_sql()
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/models/sql/compiler.py", line 848, in execute_sql
    cursor.execute(sql, params)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/utils.py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/Users/js/Documents/VirtualEnvironments/pcenv/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: relation "pc_psr_code" does not exist
LINE 1: ...escription", "pc_psr_code"."country_code_id" FROM "pc_psr_co...

Province model:

class ProvinceCode(models.Model):
    code = models.CharField(blank=False, null=False, unique=True)
    country_code = models.ForeignKey('CountryCode', blank=False, null=True)

Answer 1

You cannot execute queries during the initialization of the app registry. Your choices.py file is indirectly imported during this time, resulting in the error. To fix this issue, you can pass a callable to choices:

def get_provinces():
    province_choices = []
    for province in ProvinceCode.objects.filter(country_code_id=1).order_by('code'):
        province_choices.append((province.code, province.code))
    return province_choices

class MemberForm(forms.Form):
    provinces = forms.ChoiceField(label='Provinces', choices=get_provinces, required=True)