我正在将一个基于Django的大型应用程序从Django 1.7应用程序升级到Django 2.2，并且在与权限相关的mixin方面遇到了很多麻烦。
class PrincipalRoleRelation(models.Model):
"""A role given to a principal (user or group). If a content object is
given this is a local role, i.e. the principal has this role only for this
content object. Otherwise it is a global role, i.e. the principal has
this role generally.
user
A user instance. Either a user xor a group needs to be given.
group
A group instance. Either a user xor a group needs to be given.
role
The role which is given to the principal for content.
content
The content object which gets the local role (optional).
"""
:::
user = models.ForeignKey(User, verbose_name=_(u"User"), blank=True, null=True, on_delete=models.SET_NULL)
group = models.ForeignKey(Group, verbose_name=_(u"Group"), blank=True, null=True, on_delete=models.SET_NULL)
role = models.ForeignKey(Role, verbose_name=_(u"Role"), on_delete=models.CASCADE)
:::
但是，这在应用程序初始化期间无法加载，因为用户，组和角色等也是正在加载并且“ populate（）不能重新进入”的应用程序（所以Dango抱怨）
我试图通过修改上面的代码来解决此问题，以创建一种“骨架”类，该类不尝试引用任何其他应用，例如：
app_models_loaded = True
try:
from django.contrib.auth import get_user_model
User = get_user_model()
except:
app_models_loaded = False
if app_models_loaded:
from django.contrib.auth.models import Group
user = models.ForeignKey(User, verbose_name=_(u"User"), blank=True, null=True, on_delete=models.SET_NULL)
group = models.ForeignKey(Group, verbose_name=_(u"Group"), blank=True, null=True, on_delete=models.SET_NULL)
role = models.ForeignKey(Role, verbose_name=_(u"Role"), on_delete=models.CASCADE)
:::
然后在manage.py中，我定义了完整的mixin类，称为PrincipalRoleRelation2，并通过代码覆盖了骨架类：
from django.contrib import admin
from permissions.models import PrincipalRoleRelation
if admin.site.is_registered(PrincipalRoleRelation):
admin.site.unregister(PrincipalRoleRelation)
admin.site.register(PrincipalRoleRelation, PrincipalRoleRelation2)
但是，尽管这似乎几乎可行，但是我没有看到某些PrincipalRoleRelation2属性，例如“ role”，我希望是重新映射的PrincipalRoleRelation类，其中存在所有属性。
我觉得我正在把自己挖进一个越来越深的洞，并且上述方法是不正确的，并且永远无法正常工作。因此，任何帮助将不胜感激！
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编辑：为响应schillingt的评论，User类的定义如下：
class User(AbstractBaseUser): # , PermissionsMixin):
""" Custom user model
Currently just used by the tests for django-permissions
All unique user fields required for a user
NB: Fields that are customizable across multiple identities will be part of a Profile object
"""
# Dont use PermissionsMixin since not using contrib.auth.models.Permissions
# and not using authentication backend perms ... so its only relevant for groups
# ... however it causes user.groups relations name clashes ..
# But we are using the groups part with django-permissions:
groups = models.ManyToManyField(Group, verbose_name=_('groups'),
blank=True, help_text=_('The groups this user belongs to. A user will '
'get all permissions granted to each of '
'his/her group.'),
related_name="user_set", related_query_name="user")
is_superuser = models.BooleanField(_('superuser status'), default=False,
help_text=_('Designates that this user has all permissions without '
'explicitly assigning them.'))
username = models.EmailField(_('Email (Username)'), max_length=255, unique=True)
# Make username an email and just dummy in email here so its clearer for user.email use cases
我正在将一个基于Django的大型应用程序从Django 1.7应用程序升级到Django 2.2，并且在与权限相关的mixin方面遇到了很多麻烦。类PrincipalRoleRelation（models.Model）：“”“角色...
作为循环引用的一种解决方案，django可以指定对相关模型具有字符串引用的ForeignKey（或任何其他关系字段），而无需导入实际的类。