NoneType错误'_meta‘对象没有属性’_meta‘

Question

我正在尝试建立一个社区页面，它既包括发布新帖子的表单，也包括以前所有帖子的列表，类似于facebook。但现在我一直搞错了

'NoneType' object has no attribute '_meta'

这是我的观点功能：

def community(request):
    if redirect_if_false_choice(request):
        return redirect_if_false_choice(request)
    posts = CommunityPost.objects.filter(public=True).order_by('date_posted')
    form = PostForm(request.POST or None)
    if str(request.method) == 'GET':
       return render(request, 'officer/community.html', {'posts': posts, 'form': form})
    if form.is_valid():
       form.save()
       return redirect('community')

以下是表格：

class PostForm(forms.ModelForm):
   class Meta:
        model = CommunityPost
        fields = ('content', )
        widgets = {
            'content': forms.Textarea(attrs={'rows': 4, 'placeholder': 
            "What's going on?"})
        }

整个堆栈跟踪：

Internal Server Error: /officer/community/
Traceback (most recent call last):
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/security_officer_wanted/officer/views.py", line 114, in community
    return render(request, 'officer/community.html', {'posts': posts, 'form': form})
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/shortcuts.py", line 36, in render
    content = loader.render_to_string(template_name, context, request, using=using)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/loader.py", line 62, in render_to_string
    return template.render(context, request)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 171, in render
    return self._render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/defaulttags.py", line 209, in render
    nodelist.append(node.render_annotated(context))
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/django/template/library.py", line 192, in render
    output = self.func(*resolved_args, **resolved_kwargs)
  File "/home/christian/PycharmProjects/django-securityofficerwanted/venv/lib/python3.6/site-packages/image_cropping/templatetags/cropping.py", line 18, in cropped_thumbnail
    ratiofield = instance._meta.get_field(ratiofieldname)
AttributeError: 'NoneType' object has no attribute '_meta'
[04/Jul/2019 06:18:57] "GET /officer/community/ HTTP/1.1" 500 169040

Answer 1

我想通了，错误是网站不知道是谁发的帖子，我把它修好了，现在它起作用了。(模板调用CommunityPost模型中的一个函数，该函数应该返回发布帖子的用户。但既然没有人发出去，它就一文不名。)

Answer 2

从你提供的信息来看是不可能确定的。

向您报告的错误，毫无疑问，提到了一个行号，这将是非常有信息的，看看它，您几乎可以肯定是什么是什么意思。产生错误的行可能在Django库中，但是您可以在任何合理的调试器中跟踪堆栈，直到代码调用Django并在那里抓取头。

也就是说，一个可能与您所经历的相关的明确问题是，上面的元类不是PostForm类的成员。请参见：

https://docs.djangoproject.com/en/2.2/topics/forms/modelforms/

并尝试例如：

class PostForm(forms.ModelForm):
    class Meta:
        model = CommunityPost
        fields = ('content', )
        widgets = {
            'content': forms.Textarea(attrs={'rows': 4, 'placeholder': "What's going on?"})
        }

但我觉得这可能是你在这里的文章中的一个格式错误。很不确定。我只能说，看上去不对。