'NoneType' 类型的对象在基于 django 类的 ListView 中没有 len()

Question

我有以下视图用于显示搜索记录列表

class ListOfSearchedRecords(LoginRequiredMixin, ListView):
    template_name = 'list_of_searched_records.html'
    context_object_name = 'filtered_records'
    paginate_by = 10

    def get_queryset(self):
        """
        Returns the Records 
        """
        if self.request.method == "GET" and self.request.GET:
            if 'q' in self.request.GET:
              if self.request.GET['q']:
                keyword = self.request.GET.get('q', None)
                log.debug("Filtered keyword: %s", keyword)
                result = Product.objects.order_by('-created').filter(
                  Q(products__name__icontains=keyword))
                if result:
                  return result
                else:
                  return []

    def get_context_data(self, **kwargs):
        context = super(ListOfSearchedRecords, self).get_context_data(**kwargs)
        context.update(
           {
           'context_list':['Data_one', 'Data_two', 'Data_three']}
           )
        return context

追溯

Traceback (most recent call last):
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 115, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/views/generic/base.py", line 86, in dispatch
    return handler(request, *args, **kwargs)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/views/generic/list.py", line 139, in get
    context = self.get_context_data(object_list=self.object_list)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/views/generic/list.py", line 99, in get_context_data
    paginator, page, queryset, is_paginated = self.paginate_queryset(queryset, page_size)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/views/generic/list.py", line 53, in paginate_queryset
    page = paginator.page(page_number)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/core/paginator.py", line 40, in page
    number = self.validate_number(number)
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/core/paginator.py", line 31, in validate_number
    if number > self.num_pages:
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/core/paginator.py", line 63, in _get_num_pages
    if self.count == 0 and not self.allow_empty_first_page:
  File "/home/user/Envs/proj/local/lib/python2.7/site-packages/django/core/paginator.py", line 56, in _get_count
    self._count = len(self.object_list)
TypeError: object of type 'NoneType' has no len()

搜索表单

                            <form id="changelist-search" class="form-search" action="{% url 'filtered_list_of_records' %}" method="get">
                                <input id="searchbar" name="q" type="text" class="search_ico pull-right search_bar input-xlarge fnt16" placeholder="Search">                                    
                            </form>                                

所以当我们输入任何值进行搜索时，上面的代码是有效的，我的意思是如果q 有任何值，但是当我们提交Search form 没有任何东西时，我遇到了错误

那我为什么会得到它以及如何避免它？

Answer 1

当您没有在request.GET 中为q 填写内容时，方法get_queryset 不会返回任何内容。因此它返回None，它不是一个有效的QuerySet 或可迭代的。因此 Django 无法调用 len()。

您需要确保get_queryset 始终返回一个值：

def get_queryset(self):
    """
    Returns the Records 
    """
    if self.request.method == "GET" and self.request.GET:
        if 'q' in self.request.GET:
          if self.request.GET['q']:
            # ...
    return [] # add this line here