尝试迁移时出现 "The following content types are stale and need to be deleted"。这是什么意思，我该如何解决？

Question

这是我的 models.py:

class Notification(models.Model):
    user = models.ForeignKey(User)
    createdAt = models.DateTimeField(auto_now_add=True, blank=True)
    read = models.BooleanField(default=False, blank=True)

    class Meta:
        abstract = True

class RegularNotification(Notification):
    message = models.CharField(max_length=150)
    link = models.CharField(max_length=100)

class FNotification(Notification):
    # same as Notification
    pass

当我执行 python manage.py makemigrations 时，它是这样说的：

Migrations for 'CApp':
  0019_auto_20151202_2228.py:
    - Create model RegularNotification
    - Create model FNotification
    - Remove field user from notification
    - Add field f_request to userextended
    - Delete model Notification

首先，它说 Remove field user from notification 很奇怪，因为 user 仍然在我的 Notiication 模型中（所以如果有人能弄清楚为什么它说它说 'removing the field user from notification'，那就太好了！）但是，当我继续尝试做 python manage.py migrate 时，我收到了这条消息：

Applying CMApp.0019_auto_20151202_2228... OK
The following content types are stale and need to be deleted:

    CApp | notification

Any objects related to these content types by a foreign key will also
be deleted. Are you sure you want to delete these content types?
If you're unsure, answer 'no'.

    Type 'yes' to continue, or 'no' to cancel: no

我输入了 no。但这到底是什么意思，为什么我会收到此消息以及如何才能使我不需要此消息？

Answer 1

当您 remove/delete 一个模型并进行迁移时，您收到的消息会被触发。

在大多数情况下，您可以安全地删除它们。但是，在某些情况下，这可能会导致数据丢失。如果其他模型有被移除模型的外键，这些对象也将被删除。

Here's the django ticket that requests to make deleting stale content types safer.

编辑

正如@x-yuri 指出的那样，此问题单已修复并已在 Django 1.11 中发布。

尝试迁移时出现 "The following content types are stale and need to be deleted"。这是什么意思，我该如何解决？

Getting a "The following content types are stale and need to be deleted" when trying to do a migrate. What does this mean, and how can I solve it?

django

django-models

django-migrations

django-contenttypes