Django混合鸡肉和鸡蛋的噩梦

Question

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应用程序，并且在使用与权限相关的混入时遇到了很多问题。

   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)

       :::

然而，这无法在应用程序初始化期间加载，因为用户、组和角色等也是加载过程中的应用程序，并且"populate()不是可重入的“(因此Dango抱怨)

我试图通过修改上面的代码来解决这个问题，创建一种不试图引用任何其他应用程序的“骨架”类，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，我会定义完整的mixin类，比如PrincipalRoleRelation2，并通过下面的代码重写骨架类：

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)

然而，尽管这看起来几乎可以工作，但我没有看到一些角色属性，例如“PrincipalRoleRelation2”，在我希望的重新映射的PrincipalRoleRelation类中，所有属性都存在。

我觉得我把自己挖进了一个更深的洞里，上面的方法是不可靠的，也永远不会正常工作。因此，任何帮助都将非常感谢！

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edit:为了响应schillingt的评论，User类定义如下：

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

Answer 1

作为循环引用的解决方案，django能够使用相关模型的字符串引用来指定ForeignKey (或任何其他关系字段)，而不是导入实际的类。

user = models.ForeignKey('users.User', on_delete=models.CASCADE)

这是imo定义相关字段的推荐方式。