Django:无法从admin将ForeignKey值设置为None

null 和 blank 设置为True。问题是,当我从管理界面编辑一个类别时,我不能将ForeignKey更改为 --------- (这看起来像管理员说无的方式。)值最初可以是无,我可以通过管理员将其更改为实际值,我可以更改为另一个值,但一旦它具有实际值,我就不能将其更改回无。(即通过管理员)

为什么会这样?

这是你的密码 models.py

from django.db import models
import tinymce.models
from photologue.models import Photo

from django.utils.translation import ugettext_lazy as _
import multilingual

class SimplePage(models.Model):

    slug = models.SlugField(
        _('Slug'),
        unique=True,
        help_text=_('''Unique identifier for URL. Only letters, digits, and -.\
e.g. history-oct-2000 or about''')
    )

    category = models.ForeignKey('Category',
                                 related_name='items_including_main_page',
                                 blank=True, null=True)

    class Translation(multilingual.Translation):
        title = models.CharField(_('Title'), max_length=42)
        content = tinymce.models.HTMLField(_('Content'), blank=True)

    class Admin:
        list_display = ('title',)
        search_fields = ('title', 'content')

    class Meta:
        verbose_name = _('Simple page')
        verbose_name_plural = _('Simple pages')

    __unicode__ = lambda self: self.title


class Category(models.Model):
    main_page = models.OneToOneField(
        SimplePage,
        related_name='_SimplePage__category_which_has_this_as_title', 
        blank=True,
        null=True)

    get_title = lambda self: self.main_page.title if self.main_page else u''

    get_items = lambda self: \
        self.items_including_main_page.exclude(id__exact=self.main_page.id)

    __unicode__ = lambda self: self.get_title() or u'Titleless Category'

    class Admin:
        pass

    class Meta:
        verbose_name = _('Category')
        verbose_name_plural = _('Categories')

以及 admin.py :

from sitehelpers.models import *
from django.contrib import admin
import multilingual

class SimplePageAdmin(multilingual.ModelAdmin):
    pass

admin.site.register(SimplePage, SimplePageAdmin)

admin.site.register(Category)