「DoesNotExist：ContentType的匹配查詢不存在」只發生偶爾

Question

很簡單的代碼，但一個奇怪的情況...

有這個片段的模板：

{% is_contest story as iscontest %} 

其中is_contest這是自定義模板標籤：

@register.assignment_tag 
def is_contest(obj): 
    contesttype = ContentType.objects.get_for_model(Contest) 
    return obj.source_content_type == contesttype 

但是比賽是在django_content_type表中。

最古怪的部分：這只是一個間歇性的錯誤，而且似乎只是由模板標籤引起的（我也是在視圖中檢查這個選項，但是沒有錯誤）。

任何想法？

編輯：全回溯

Traceback (most recent call last): 

    File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py", line 111, in get_response 
    response = callback(request, *callback_args, **callback_kwargs) 

    File "/home/ubuntu/src/cbframe/commentableobjects/views/commentableobject_list.py", line 142, in commentablobject_list 
    return render_to_response('commentableobjects-list.html', info, context_instance=RequestContext(request)) 

    File "/usr/local/lib/python2.7/dist-packages/django/shortcuts/__init__.py", line 20, in render_to_response 
    return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/loader.py", line 176, in render_to_string 
    return t.render(context_instance) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 140, in render 
    return self._render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 134, in _render 
    return self.nodelist.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 823, in render 
    bit = self.render_node(node, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py", line 74, in render_node 
    return node.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py", line 123, in render 
    return compiled_parent._render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 134, in _render 
    return self.nodelist.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 823, in render 
    bit = self.render_node(node, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py", line 74, in render_node 
    return node.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py", line 62, in render 
    result = block.nodelist.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 823, in render 
    bit = self.render_node(node, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py", line 74, in render_node 
    return node.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py", line 281, in render 
    return nodelist.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 823, in render 
    bit = self.render_node(node, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py", line 74, in render_node 
    return node.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py", line 155, in render 
    return self.render_template(self.template, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py", line 137, in render_template 
    output = template.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 140, in render 
    return self._render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 134, in _render 
    return self.nodelist.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 823, in render 
    bit = self.render_node(node, context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/debug.py", line 74, in render_node 
    return node.render(context) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/defaulttags.py", line 185, in render 
    nodelist.append(node.render(context)) 

    File "/usr/local/lib/python2.7/dist-packages/django/template/base.py", line 1139, in render 
    context[self.target_var] = func(*resolved_args, **resolved_kwargs) 

    File "/home/ubuntu/src/cbframe/commentableobjects/templatetags/url_target_blank.py", line 27, in is_contest 
    return obj.source_content_type == contesttype 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py", line 350, in __get__ 
    rel_obj = qs.get(**params) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 366, in get 
    % self.model._meta.object_name) 

DoesNotExist: ContentType matching query does not exist. 

Answer 1

一個問題可能是您比較2個實例與海誓山盟，而這些應該是在Django相同的，因爲Django的緩存他們，這不是一個保證。

不知道如何/在哪裏的source_content_type從何而來，但我會建議這個：

return isinstance(obj, contesttype) 

至於原來的問題，你有一個堆棧跟蹤？這個錯誤似乎有點奇怪。

你確定Contest沒有被覆蓋在範圍的某個地方嗎？ Contest可能被模塊中的其他代碼覆蓋，那麼最有可能的嫌疑人將是global Contest，但在這裏似乎並不是這樣。

由於堆棧跟蹤問題有點清晰。

這部分明確表明，它會錯在obj.source_content_type部分：

return obj.source_content_type == contesttype 

我覺得有些對象不具有現有source_content_type了。