int()函数出现无效字面值异常原因：

Question

当我尝试访问类别 category1-test 时，出现了一个错误：无效的字面量，无法将 'category1-test' 转换为整数。我不明白这个错误的原因。

模型

class Category(models.Model):
    title = models.CharField(max_length=200)
    description = models.CharField(max_length=500)
    slug = models.SlugField(max_length=300, unique=True)

    def __str__(self):
        return '%s%s' % (self.title, self.description)

    class Meta:
        verbose_name_plural = 'Categories'

    @models.permalink
    def get_absolute_url(self):
       return ('category-detail', (), {'category_id': str(self.slug)})





class Info(models.Model):
    ...
    category = models.ForeignKey(Category)

    @models.permalink
    def get_absolute_url(self):
        return ('category_info', (), {'info_id': str(self.id)})

视图

def view_list(request, category_id):
    list = Info.objects.filter(category = category_id).order_by("-created")
    list = pagination(request, list, 10)
    category = get_object_or_404(Category, slug=category_id)
    return render_to_response('view_list.html', add_csrf(request, list=list, slug=category_id, category=category), context_instance=Reque
stContext(request))


Traceback:
File "/usr/local/lib/python3.2/dist-packages/django/core/handlers/base.py" in get_response
  114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/usr/info/views.py" in view_list
  41.     list = Info.objects.filter(category = category_id).order_by("-created")
File "/usr/local/lib/python3.2/dist-packages/django/db/models/manager.py" in filter
  163.         return self.get_queryset().filter(*args, **kwargs)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/query.py" in filter
  590.         return self._filter_or_exclude(False, *args, **kwargs)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/query.py" in _filter_or_exclude
  608.             clone.query.add_q(Q(*args, **kwargs))
File "/usr/local/lib/python3.2/dist-packages/django/db/models/sql/query.py" in add_q
  1198.         clause = self._add_q(where_part, used_aliases)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/sql/query.py" in _add_q
  1232.                     current_negated=current_negated)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/sql/query.py" in build_filter
  1122.                                                      lookup_type, value)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/fields/related.py" in get_lookup_constraint
  1105.                      value[index]), AND)
File "/usr/local/lib/python3.2/dist-packages/django/utils/tree.py" in add
  104.         data = self._prepare_data(data)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/sql/where.py" in _prepare_data
  79.             value = obj.prepare(lookup_type, value)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/sql/where.py" in prepare
  352.             return self.field.get_prep_lookup(lookup_type, value)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/fields/__init__.py" in get_prep_lookup
  369.             return self.get_prep_value(value)
File "/usr/local/lib/python3.2/dist-packages/django/db/models/fields/__init__.py" in get_prep_value
  613.         return int(value)

错误类型：在 /category1-test 处发生了 ValueError
错误信息：无效的字面量，无法将 'category1-test' 转换为整数

Answer 1

category_id 看起来像是从网址中提取出来的字符串，比如 "category1_test"，但是你却想把它当作外键来用（外键通常是整数类型 int）。你可以这样做：

lst = Info.objects.filter(category__slug=category_id).order_by("-created")

或者，可以重新排列一下：

category = get_object_or_404(Category, slug=category_id)
lst = Info.objects.filter(category=category).order_by("-created")

（注意：如果我是你，我不会把变量命名为 "list"。这样会把内置的 list 给覆盖掉！）