无法使用django-nested-inline生成添加新的内联django模型按钮

Question

看看代码 -

models.py

from __future__ import unicode_literals
from django.db import models
from django.contrib.auth.models import User

class Event(models.Model):
        _id = models.AutoField(primary_key=True)
        name = models.CharField(max_length=100)
        primary_link = models.URLField(max_length=400, null=True, blank=True)
        def __unicode__(self):
                return self.name
class EventMedia(models.Model):
        event = models.ForeignKey(Event)
        description = models.TextField(null=True, blank=True)
        media = models.FileField(null=True, blank=True, upload_to="event_media")
        def __unicode__(self):
                return self.event.name

和

admin.py

from django.contrib import admin
from mainapi.models import *
from nested_inline.admin import NestedStackedInline, NestedModelAdmin

class EventMediaInline(NestedStackedInline):
        model = EventMedia
        extra = 1
class coreEventsAdmin(NestedModelAdmin):
        inlines = (EventMediaInline,)

admin.site.register(Event, coreEventsAdmin)

现在管理网站上发生了什么，我能够在事件模型上看到EventMedia模型的内联块，但是我无法看到在事件模型中添加事件媒体的新内联块的选项。有谁知道它可能是什么原因？