运行 make 迁移时出现 Django 关系错误

问题描述

嘿，我正在尝试初始化一个新数据库，但在设置迁移时遇到了一些问题.我得到的错误似乎源于设置我的表格.在我使用的表单中，我正在创建一个选择字段:

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)

PROVINCE_CHOICES 来自这里:

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))

问题似乎是在迁移发生之前调用了这个循环，给我一个错误，指出省模型不存在.注释掉对该文件的引用允许迁移工作，但是，这似乎是继续使用的不切实际的解决方案.有没有办法绕过这个错误?

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?

作为参考，这是我在运行 manage.py makemigrations 时遇到的错误:

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...

省模型:

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

推荐答案

在应用注册表初始化期间，您无法执行查询.您的 choices.py 文件在此期间被间接导入，导致错误.要解决此问题，您可以将可调用对象传递给 choices:

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)

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