Django admin says SuspiciousOperation, filtering not allowed

Question

I have 3 related models in my system. Each user belongs to a particular place. Users can send messages, and comment on messages, kind of like forum threads.

Here are the 3 models:

class Place(models.Model):
    name = models.CharField(max_length=50, unique=True)
    slug = models.SlugField(max_length=50, unique=True)

class Message(models.Model):
    creator = models.ForeignKey(User)
    title = models.CharField(max_length=40) 
    content = models.CharField(max_length=3000)
    date_created = models.DateTimeField(default=timezone.now)  
    place = models.ForeignKey(Place)

class Comment(models.Model):
    creator = models.ForeignKey(User)
    content = models.CharField(max_length=3000)
    date_created = models.DateTimeField(default=timezone.now)  
    message = models.ForeignKey(Message)

I want this structure to be reflected in my AdminModels. So for my PlaceAdmin I wrote this:

class PlaceAdmin(admin.ModelAdmin):
    list_display = ('name', 'slug', 'list_messages')

    def list_messages(self, obj):
        url = reverse('admin:user_content_message_changelist')
        return '<a href="{0}?place__id__exact={1}">List messages</a>'.format(url, obj.id)

    list_messages.allow_tags = True
    list_messages.short_description = 'Messages'

This works perfectly, each place links to a list of messages filtered by that place. So I did the same for my MessageAdmin :

class MessageAdmin(admin.ModelAdmin):
    list_display = ('title', 'list_comments')

    def list_comments(self, obj):
        url = reverse('admin:user_content_comment_changelist')
        return '<a href="{0}?message__id__exact={1}">List comments</a>'.format(url, obj.id)

    list_comments.allow_tags = True
    list_comments.short_description = 'Comments'

And I get the following error:

SuspiciousOperation at /admin/user_content/comment/
Filtering by message__id__exact not allowed

I don't understand why one is allowed and the other isn't. Any ideas? I'm using Django 1.5.

Answer 1

我意识到自己犯了一个错误-此处显示的代码经过了简化，而Message模型实际上是从抽象的Content模型继承的，所以我需要注释列表的URL为：

<a href="{0}?message__content_ptr__exact={1}">List comments</a>